PERITONEAL DIALYSIS SYSTEM AND METHOD EMPLOYING PUMPING CASSETTE

Abstract: Peritoneal dialysis systems and methods apply fluid pressure to move liquid. The systems and methods can emulate either a fixed head height condition or different head height conditions, independent of the actual head height differential between the patient's peritoneal cavity and the external liquid source or destination. The systems and methods can also switch between low-relative pressure flow mode when considerations of patient comfort and safety predominate and a high-relative pressure flow mode when considerations of processing speed predominate.

Description: PERITONEAL DIALYSIS SYSTEM AND METHOD EMPLOYING PUMPING CASSETTE Field of the Invention This invention relates to systems and meth¬ ods for performing peritoneal dialysis. Background of the Invention Peritoneal Dialysis (PD) periodically infuses sterile aqueous solution into the peritoneal cavity. This solution is called peritoneal dialysis solution, or dialysate. Diffusion and osmosis exchanges take place between the solution and the bloodstream across the natural body membranes. These exchanges remove the waste products that the kidneys normally excrete. The waste products typically consist of solutes like sodium and chloride ions, and the other compounds normally excreted through the kidneys like urea, creatinine, and water. The diffusion of water across the peritoneal membrane during dialysis is called ultrafiltration. Conventional peritoneal dialysis solutions include dextrose in concentrations sufficient to generate the necessary osmotic pressure to remove water from the patient through ultrafiltration. Continuous Ambulatory Peritoneal Dialysis (CAPD) is a popular form of PD. A patient performs CAPD manually about four times a day. During CAPD, the patient drains spent peritoneal dialysis solution from his/her peritoneal cavity. The patient then infuses fresh peritoneal dialysis solution into his/her peritoneal cavity. This drain and fill procedure usually takes about 1 hour. Automated Peritoneal Dialysis (APD) is an¬ other popular form of PD. APD uses a machine, called a cycler, to automatically infuse, dwell, and drain peritoneal dialysis solution to and from the patient's peritoneal cavity. APD is particularly attractive to a PD patient, because it can be performed at night while the patient is asleep. This frees the patient from the day-to-day demands of CAPD during his/her waking and working hours. The APD sequence typically last for several hours. It often begins with an initial drain cycle to empty the peritoneal cavity of spent dialysate. The APD sequence then proceeds through a succession of fill, dwell, and drain phases that follow one after the other. Each fill/dwell/drain sequence is called a cycle. During the fill phase, the cycler transfers a predetermined volume of fresh, warmed dialysate into the peritoneal cavity of the patient. The dialysate remains (or "dwells") within the peritoneal cavity for a time. This is called the dwell phase. During the drain phase, the cycler removes the spent dialysate from the peritoneal cavity. The number of fill/dwell/drain cycles that are required during a given APD session depends upon the total volume of dialysate prescribed for the patient's APD regime. APD can be and is practiced in different ways. Continuous Cycling Peritoneal Dialysis (CCPD) is one commonly used APD modality. During each fill/dwell/drain phase of CCPD, the cycler infuses a prescribed volume of dialysate. After a prescribed dwell period, the cycler completely drains this liquid volume from the patient, leaving the peritoneal cavity empty, or "dry." Typically, CCPD employs 6 fill/dwell/drain cycles to achieve a prescribed therapy volume. After the last prescribed fill/dwell/drain cycle in CCPD, the cycler infuses a final fill volume. The final fill volume dwells in the patient through the day. It is drained at the outset of the next CCPD session in the evening. The final fill volume can contain a different concentration of dextrose than the fill volume of the successive CCPD fill/dwell/drain fill cycles the cycler provides. Intermittent Peritoneal Dialysis (IPD) is another APD modality. IPD is typically used in acute situations, when a patient suddenly enters dialysis therapy. IPD can also be used when a patient requires PD, but cannot undertake the responsibilities of CAPD or otherwise do it at home. Like CCPD, IPD involves a series of fill/dwell/drain cycles. The cycles in IPD are typically closer in time than in CCPD. In addition, unlike CCPD, IPD does not include a final fill phase. In IPD, the patient's peritoneal cavity is left free of dialysate (or "dry") in between APD therapy sessions. Tidal Peritoneal Dialysis (TPD) iε another APD modality. Like CCPD, TPD includes a series of fill/dwell/drain cycles. Unlike CCPD, TPD does not completely drain dialysate from the peritoneal cavity during each drain phase. Instead, TPD estab- lishes a base volume during the first fill phase and drains only a portion of this volume during the first drain phase. Subsequent fill/dwell/drain cycles infuse then drain a replacement volume on top of the base volume, except for the last drain phase. The last drain phase removes all dialysate from the peritoneal cavity. There is a variation of TPD that includeε cycles during which the patient is completely drained and infused with a new full base volume of dialysis. TPD can include a final fill cycle, like CCPD. Alternatively, TPD can avoid the final fill cycle, like IPD. APD offers flexibility and quality of life enhancements to a person requiring dialysis. APD can free the patient from . the fatigue and inconvenience that the day to day practice of CAPD represents to some individuals. APD can give back to the patient his or her waking and working hours free of the need to conduct dialysiε exchangeε. Still, the complexity and size of past machines and associated disposables for various APD modalities have dampened widespread patient acceptance of APD as an alternative to manual peritoneal dialysis methods. Summary of the Invention The invention provides improved systems and methods for performing peritoneal dialysis. According to one aspect of the invention, the improved systems and methods serve to establish flow communication with the patient's peritoneal cavity through a pumping mechanism that compriseε a pump chamber and a diaphragm. The systems and methods emulate a selected gravity flow condition by applying fluid pressure to the diaphragm to operate the pump chamber to either move dialysis solution from the peritoneal cavity or move dialysis solution into the peritoneal cavity. Systems and methods that incorporate this aspect of the invention can emulate either a fixed head height condition or different head height conditions. The systems and methods are able to emulate a selected head height differential regardless of the actual head height differential existing between the patient's peritoneal cavity and the external liquid source or destination. According to another aspect of the invention, different fluid pressure modes can be used to operate the pumping mechanism. The improved systems and methods can rapidly switch during a given peritoneal dialysis procedure between a low- relative pressure mode and a high-relative pressure mode. The low-relative pressure mode is selected during patient infusion and drain phases, when considerations of patient comfort and safety predominate. The high-relative pressure mode iε selected during transfers of liquid from supply bags to the heater bag, when considerations of processing speed predominate. In a preferred embodiment, the systems and methods apply pneumatic fluid pressure. The preferred arrangement applies pneumatic fluid pressures that are both above and below atmospheric pressure and that vary between high and low relative pressure conditions. Another aspect of the invention provides an actuator having a chamber that conveys pneumatic pressure to the diaphragm for moving liquid through the pumping mechanism. According to this aspect of the invention, an insert occupies the chamber. The insert helps dampen and direct the pneumatic pressure upon the diaphragm, negating transient thermal effects that may arise during the conveyance of pneumatic pressure. In a preferred embodiment, the insert is made of an open cell porous material. Another aspect of the invention periodically measures fluid pressure in the actuator chamber to derive liquid volumes moved by the pump chamber. Other features and advantages of the inventions are set forth in the following specification and attached drawings. Brief Description of the Drawings Fig. 1 is a perspective view an automated peritoneal dialysis system that embodies the features of the invention, with the associated disposable liquid delivery set ready for use with the associated cycler; Fig. 2 is a perspective view of the cycler associated with the system shown in Fig. 1, out of association with the disposable liquid delivery set; Fig. 3 is a perspective view of the disposable liquid delivery set and attached cassette that are associated with the system shown in Fig. 1; Figs. 4 and 5 are perspective views of the organizer that is associated with the set shown in Fig. 3 in the procesε of being mounted on the cycler; Figs. 6 and 7 are perspective views of loading the disposable cassette attached to the set shown in Fig. 3 into the cycler for use; Fig. 8 is an exploded perspective view of one side of the casεette attached to the diεposable set shown in Fig. 3; Fig. 8A iε a plan view of the one εide of the cassette shown in Fig. 8, showing the liquid paths within the cassette; Fig. 8B is a plan view of the other side of the cassette shown in Fig. 8, showing the pump chambers and valve stations within the cassette; Fig. 8C is an enlarged side section view of a typical cassette valve station shown in Fig. 8B; Fig. 9 is perspective view of the cycle shown in Fig. 2 with its housing removed to show its interior; Fig. 10 is an exploded perspective view showing the main operating modules housed within the interior of the cycler; Fig. 11 iε an enlarged perεpective view of the cassette holder module housed within the cycler; Figs. 12A and 12B are exploded views of the cassette holder module shown in Fig. 11; Fig. 13 iε a perεpective view of the operative front εide of the fluid preεεure piston housed within the cassette module shown in Fig. 11; Fig. 14A is a perspective view of the back side of the fluid presεure piεton εhown in Fig. 13; Fig. 14B is a perspective view of an alternative, preferred embodiment of a fluid pressure piston that can be used with the system shown in Fig. 1; Figε. 15A and 15B are top sectional views taken generally along line 15A-15A in Fig. 11, showing the interaction between the presεure plate assembly and the fluid pressure piston within the module shown in Fig. 11, with Fig. 15A showing the presεure plate holding the piston in an at rest position and Fig. 15B showing the presεure plate holding the piεton in an operative position against the cassette; Figs. 16A and 16B are εide sectional view of the operation of the occluder assembly housed within the module shown in Fig. 11, with Fig. 16A showing the occluder assembly in a position allowing liquid flow and Fig. 16B showing the occluder asεembly in a position blocking liquid flow; Fig. 17 is a perspective view of the fluid pressure manifold module housed within the cycler; Fig. 18 is an exploded perspective view of interior of the fluid pressure manifold module shown in Fig. 17; Fig. 19 iε an exploded perspective view of the manifold assembly housed within the module shown in Fig. 18; Fig. 20 iε a plan view of the interior of the baεe plate of the manifold aεεembly shown in Fig. 19, showing the paired air ports and air conduction pathways formed therein; Fig. 21 iε a plan view of the outside of the base plate of the manifold asεembly εhown in Fig. 19, also showing the paired air ports; Fig. 22 is an exploded perεpective view of the attachment of a pneumatic valve on the outside of the baεe plate of the manifold assembly shown in Fig. 19, in registry over a pair of air ports; Fig. 23 is a schematic view of the pressure supply εyεtem aεεociated with the air regulation system that the manifold asεembly εhown in Fig. 19 defines; Fig. 24 is a schematic view of the entire air regulation system that the manifold assembly εhown in Fig. 19 defineε; Fig. 25 iε a flow chart showing the operation of the main menu and ultrafiltration review interfaceε that the controller for the cycler shown in Fig. 1 employs; Fig. 26 is a flow chart showing the operation of the therapy εelection interfaces that the controller for the cycler shown in Fig. l employs; Fig. 27 is a flow chart showing the operation of the set up interfaces that the controller for the cycler shown in Fig. 1 employs; Fig. 28 is a flow chart showing the operation of the run time interfaces that the controller for the cycler εhown in Fig. l employs; Fig. 29 is a flow chart showing the operation of the background monitoring that the controller for the cycler shown in Fig. 1 employs; Fig. 30 is a flow chart showing the operation of the alarm routines that the controller for the cycler shown in Fig. 1 employs; Fig. 31 is a flow chart showing the operation of the post therapy interfaces that the controller for the cycler shown in Fig. 1 employs; Fig. 32 is a diagrammatic representation of sequence of liquid flow through the casεette governed by the cycler controller during a typical fill phaεe of an APD procedure; Fig. 33 iε a diagrammatic repreεentation of εequence of liquid flow through the cassette governed by the cycler controller during a dwell phase (replenish heater bag) of an APD procedure; Fig. 34 is a diagrammatic representation of sequence of liquid flow through the casεette governed by the cycler controller during a drain phase of an APD procedure; and Fig. 35 is a diagrammatic repreεentation of sequence of liquid flow through the cassette governed by the cycler controller during a last dwell of an APD procedure. The invention may be embodied in several forms without departing from itε εpirit or essential characteristicε. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All em¬ bodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims. Description of the Preferred Embodiments Fig. 1 shows an automated peritoneal dialy¬ sis system 10 that embodies the features of the invention. The system 10 includes three principal components. These are a liquid supply and delivery set 12; a cycler 14 that interacts with the delivery set 12 to pump liquid through it; and a controller 16 that governs the interaction to perform a selected APD procedure. In the illustrated and preferred embodiment, the cycler and controller are located within a common housing 82. The cycler 14 is intended to be a durable item capable of long term, maintenance free use. Aε Fig. 2 shows, the cycler 14 also presents a compact footprint, suited for operation upon a table top or other relatively small surface normally found in the home. The cycler 14 is also lightweight and por¬ table. The εet 12 is intended to be a single use, disposable item. The user loads the set 12 on the cycler 14 before beginning each APD therapy session. The user removeε the set 12 from the cycler 14 upon the completing the therapy session and discards it. In use (as Fig. 1 shows) , the user connects the set 12 to his/her indwelling peritoneal catheter 18. The user also connects the set 12 to individual bags 20 containing sterile peritoneal dialysis solution for infusion. The set 12 also connects to a bag 22 in which the dialysis solution is heated to a desired temperature (typically to about 37 degrees C) before infusion. The controller 16 paces the cycler 14 through a prescribed series of fill, dwell, and drain cycles typical of an APD procedure. During the fill phase, the cycler 14 infuses the heated dialysate through the set 12 and into the patient's peritoneal cavity. Following the dwell phaεe, the cycler 14 institutes a drain phase, during which the cycler 14 dischargeε εpent dialysis solution from the patient'ε peritoneal cavity through the set into a nearby drain (not shown) . As Fig. 1 shows, the cycler 14 does not re¬ quire hangers for suspending the source solution bags 20 at a prescribed head height above it. This is because the cycler 14 is not a gravity flow system. Instead, using quiet, reliable pneumatic pumping action, the cycler 14 emulates gravity flow, even when the source solution bags 20 lie right alongεide it, or in any other mutual orientation. The cycler 14 can emulate a fixed head height during a given procedure. Alternatively, the cycler 14 can change the head height to either in- creaεe or decreaεe the rate of flow during a proce¬ dure. The cycler 14 can emulate one or more selected head height differentials regardleεε of the actual head height differential exiεting between the patient'ε peritoneal cavity and the external liquid εourceε or destinations. Because the cycler 14 establishes esεentially an artificial head height, it has the flexibility to interact with and adapt quickly to the particular physiology and relative elevation of the patient. The compact nature and silent, reliable op- erating characteristicε of the cycler 14 make it ideally suited for bedside use at home while the patient is asleep. The principal system components will now be individually diεcuεεed in greater detail. I. THE DISPOSABLE SET Aε Fig. 3 best shows, the set 12 includes a cassette 24 to which lengths of flexible plastic tubes 26/28/30/32/34 are attached. Fig. 3 εhowε the diεpoεable liquid supply and delivery set 12 before it is readied for use in association with the cycler 14. Fig. 1 shows the dispoεable set 12 when readied for use in aεεociation with the cycler 14. In use (as Fig. 1 shows) , the distal ends of the tubes 26 to 34 connect outside the cycler 14 to the bags 20 of fresh peritoneal dialysiε solution, to the liquid heater bag 22, to the patient's indwelling catheter 18, and to a drain (not shown) . For this reason, the tube 34 carries a con¬ ventional connector 36 for attachment to the patient's indwelling catheter 18. Other tubes 26/30/32 carry conventional connectors 38 for attachment to bag ports. Tube 32 contains a Y- connector 31, creating tubing branches 32A and 32B, each of which may connect to a bag 20. The set 12 may contain multiple branches to accommodate attachment to multiple bags 20 of dialysis solution. The tube 28 has a drain connector 39. It serves to discharge liquid into the external drain (not shown) . The tubing attached to the set carries an inline, manual clamp 40, except the drain tube 28. As Figε. 1 and 3 εhow, the set 12 also preferably includes a branch connector 54 on the drain tube 28. The branch connector 54 creates a tubing branch 28A that carrieε a connector 55. The connector 55 attaches to a mating connector on an effluent inspection bag (not shown) . Once attached, the patient can divert a volume (about 25 ml) of spent dialysate through branch 28A into the inspection bag during the first drain cycle. The bag allows the patient to inspect for cloudy effluent, which is an indication of peritonitis. As Figs. 6 and 7 show, in use, the cassette 24 mounts inside a holder 100 in the cycler 14 (see Fig. 1, too) . The details of the holder 100 will be discussed in greater detail later. The holder 100 orients the cassette 24 for use vertically, aε Fig. 7 shows. As Figs. 3 to 5 show, the set 12 preferably in¬ cludes an organizer 42 that holdε the diεtal tube ends in a neat, compact array. This simplifies handling and shortens the set up time. The organizer 42 includes a body with a εeries of slotted holders 44. The slotted holders 44 receive the distal tube ends with a friction fit. The organizer 42 includes slot 46 that mates with a tab 48 carried on outεide of the caεεette holder 100. A pin 50 on the outside of the cassette holder 100 also mates with an opening 52 on the organizer 42. Theεe attach the organizer 42 and attached tube ends to the outside of the cassette holder 100 (aε Figs 1 and 5 show) . Once attached, the organizer 42 frees the user's hands for making the required connections with the other elements of the cycler 14. Having made the required connectionε, the user can remove and discard the organizer 42. The caεsette 24 serves in association with the cycler 14 and the controller 16 to direct liquid flow among the multiple liquid sources and destinationε that a typical APD procedure requireε. Aε will be deεcribed in greater detail later, the caεεette 24 provideε centralized valving and pumping functions in carrying out the selected APD therapy. Figs. 8/8A/8B show the details of the cassette 24. As Fig. 8 shows, the casεette 24 includeε an injection molded body having front and back sides 58 and 60. For the purposes of description, the front side 58 is the side of the caεεette 24 that, when the cassette 24 is mounted in the holder 100, faces away from the user. A flexible diaphragm 59 and 61 overlies the front side and back sides 58 and 60 of the casεette 24, reεpectively. The cassette 24 is preferably made of a rigid medical grade plastic material. The diaphragms 59/61 are preferably made of flexible sheetε of medical grade plastic. The diaphragms 59/61 are sealed about their peripheries to the peripheral edges of the front and back sides 58/60 of the cassette 24. The casεette 24 forms an array of interior cavitieε in the εhapeε of wellε and channelε. The interior cavitieε create multiple pump chamberε Pl and P2 (viεible from the front εide 58 of the caεεette 24, as Fig. 8B showε) . The interior cavitieε also create multiple paths FI to F9 to convey liquid (visible from the back side 60 of the caεsette 24, aε Figε. 8 and 8A showε) . The interior cavities also create multiple valve stations VI to V10 (visible from the front side 58 of the cassette 24, as Fig. 8B shows) . The valve stations VI to V10 interconnect the multiple liquid pathε FI to F9 with the pump chamberε Pl and P2 and with each other. The number and arrangement of the pump cham- bers, liquid paths, and valve stations can vary. A typical APD therapy session usually requireε five liquid sources/deεtinationε. The caεεette 24 that embodies the features of the invention provides these connections with five exterior liquid lines (i.e., the flexible tubes 26 to 32) , two pump chambers Pl and P2, nine interior liquid paths FI to F9, and ten valve stations VI to V10. The two pump chambers Pl and P2 are formed aε wells that open on the front side 58 of the casεette 24. Upstanding edges 62 peripherally surround the open wells of the pump chambers Pl and P2 on the front side 58 of the cassette 24 (see Fig. 8B) . The wells forming the pump chambers Pl and P2 are closed on the back side 60 of the cassette 24 (see Fig. 8) , except that each pump chamber Pl and P2 includes a vertically spaced pair of through holes or portε 64/66 that extend through to the back εide 60 of the caεεette 24. As Figs. 8/8A/8B show, vertically spaced ports 64(1) and 66(1) are associated with pump chamber Pl. Port 64(1) communicates with liquid path F6, while port 66(1) communicates with liquid path F8. As Figs. 8/8A/8B also εhow, vertically εpaced portε 64(2) and 66(2) are aεεociated with pump chamber P2. Port 64(2) communicateε with liquid path F7, while port 66(2) communicates with liquid path F9. Aε will become apparent, either port 64(1)/ (2) or 66(1)/ (2) can serve its aεεociated chamber P1/P2 aε an inlet or an outlet. Alternatively, liquid can be brought into and discharged out of the chamber P1/P2 through the same port associated 64(1)/ (2) or 66(l)/(2). In the illustrated and preferred embodiment, the ports 64/66 are spaced εo that, when the cassette 24 is oriented vertically for use, one port 64(1)/ (2) iε located higher than the other port 66(1)/ (2) aεεociated with that pump chamber P1/P2. Aε will be deεcribed in greater detail later, this orientation provides an important air removal function. The ten valve stationε VI to VIO are likewise formed as wellε open on the front εide 58 of the caεεette 24. Fig. 8C εhowε a typical valve station V j ^. Aε Fig. 8C best showε, upεtanding edgeε 62 peripherally surround the open wellε of the valve εtationε VI to VIO on the front εide 58 of the cassette 24. As Fig. 8C best shows, the valve stationε VI to VIO are cloεed on the back side 60 of the cassette 24, except that each valve station V N includes a pair of through holes or ports 68 and 68'. One port 68 communicates with a selected liquid path F N on the back εide 60 of the cassette 24. The other port 68' communicates with another selected liquid path F j v j' on the back side 60 of the cassette 24. In each valve station V N , a raised valve seat 72 surrounds one of the ports 68. As Fig. 8C best shows, the valve seat 72 terminates lower than the surrounding peripheral edges 62. The other port 68' is flush with the front εide 58 of the cassette. As Fig. 8C continues to show best, the flexible diaphragm 59 overlying the front side 58 of the cassette 24 rests against the upstanding peripheral edges 62 surrounding the pump chambers and valve stations. With the application of positive force uniformly against this side 58 of the cassette 24 (as shown by the f-arrows in Fig. 8C) , the flexible diaphragm 59 seats against the upstanding edges 62. The positive force forms peripheral seals about the pump chambers Pl and P2 and valve stations VI to VIO. This, in turn, isolates the pump chambers Pl and P2 and valve stationε VI to VIO from each other and the rest of the system. The cycler 14 applies positive force to the front casεette side 58 for this very purpose. Further localized application of positive and negative fluid presεures upon the regionε of the diaphragm 59 overlying these peripherally sealed areas serve to flex the diaphragm regionε within theεe peripherally sealed areas. These localized applications of positive and negative fluid presεureε on the diaphragm regions overlying the pump chambers Pl and P2 εerve to move liquid out of and into the chamberε Pl and P2. Likewiεe, theεe localized applicationε of positive and negative fluid pressure on the diaphragm regionε overlying the valve εtationε VI to VIO will serve to seat and unεeat theεe diaphragm regions against the valve seats 72, thereby closing and opening the associated valve port 68. Fig. 8C showε in solid and phantom lines the flexing of the diaphragm 59 relative to a valve seat 72. In operation, the cycler 14 applies localized poεitive and negative fluid preεεureε to the diaphragm 59 for opening and cloεing the valve portε. The liquid pathε FI to F9 are formed aε elon- gated channelε that are open on the back side 60 of the cassette 2 . Upstanding edges 62 peripherally surround the open channels on the back side 60 of the cassette 24. The liquid paths FI to F9 are closed on the front side 58 of the cassette 24, except where the channels cross over valve station portε 68/68'or pump chamber portε 64(1)/ (2) and 66(1)/ (2) . The flexible diaphragm 61 overlying the back side 60 of the cassette 24 restε againεt the upstanding peripheral edges 62 surrounding the liquid pathε FI to F9. With the application of poεitive force uniformly againεt thiε side 60 of the cassette 24, the flexible diaphragm 61 seats againεt the upstanding edges 62. This forms peripheral sealε along the liquid pathε FI to F9. In operation, the cycler 14 alεo applieε positive force to the diaphragm 61 for this very purpose. As Figs. 8/8A/8B show, five premolded tube connectorε 27/29/31/33/35 extend out along one εide edge of the cassette 24. When the cassette 24 is vertically oriented for use, the tube connectors 27 to 35 are vertically stacked one above the other. The first tube connector 27 is the uppermost connector, and the fifth tube connector 35 iε the lowermoεt connector. This ordered orientation of the tube connectors 27 to 35 provides a centralized, compact unit. It also makes it possible to cluster the valve εtations within the caεεette 24 near the tube connectors 27 to 35. The first through fifth tube connectors 27 to 35 communicate with interior liquid pathε FI to F5, respectively. These liquid paths FI to F5 constitute the primary liquid paths of the cassette 24, through which liquid enters or exits the cassette 24. The remaining interior liquid paths F6 to F9 of the cassette 24 constitute branch pathε that link the primary liquid pathε FI to F5 to the pump chambers Pl and P2 through the valve stations VI to VIO. Because the pump chambers Pl and P2 are ver¬ tically oriented during use, air entering the pump chambers P1/P2 during liquid pumping operations will accumulate near the upper port 64 in each pump chamber P1/P2. The liquid pathε FI to F9 and the valve sta¬ tions VI to VIO are purposefully arranged to isolate the patient's peritoneal cavity from the air that the pump chamberε P1/P2 collect. They are also purposefully arranged so that this collected air can be transferred out of the pump chambers P1/P2 during use. More particularly, the casεette 24 isolates selected interior liquid paths from the upper portε 64 of the pump chambers Pl and P2. The cassette 24 thereby isolates these selected liquid paths from the air that accumulates in the pump chambers P1/P2. Theεe air-iεolated liquid pathε can be uεed to convey liquid directly into and from the patient'ε peritoneal cavity. The caεεette 24 alεo connectε other selected liquid paths only to the upper ports 64(1)/ (2) of the pump chamberε Pl and P2. Theεe liquid pathε can be uεed to tranεfer air out of the respective pump chamber P1/P2. Theεe liquid pathε can also be used to convey liquid away from the patient to other connected elements in the system 10, like the heater bag 22 or the drain. In this way, the caεεette 24 serves to discharge entrapped air through establiεhed noncritical liquid paths, while isolating the critical liquid paths from the air. The cassette 24 thereby keeps air from entering the patient's peritoneal cavity. More particularly, valve stations VI to V4 serve only the upper ports 64(1)/ (2) of both pump chambers Pl and P2. These valve stations VI to V4, in turn, serve only the primary liquid paths FI and F2. Branch liquid path F6 links primary paths FI and F2 with the upper port 64(1) of pump chamber Pl through valve stations VI and V2. Branch liquid path F7 links primary pathε FI and F2 with the upper port 64(2) of pump chamber P2 through valve stations V3 and V4. These primary paths FI and F2 can thereby serve aε noncritical liquid paths, but not aε critical liquid pathε, εince they are not isolated from air entrapped within the pumping chambers P1/P2. By the same token, the primary paths FI and F2 can serve to convey entrapped air from the pump chamberε Pl and P2. Tubeε that, in use, do not directly convey liquid to the patient can be connected to the noncritical liquid pathε FI and F2 through the upper two connectorε 27 and 29. One tube 26 conveys liquid to and from the heater bag 22. The other tube 28 conveys spent peritoneal εolution to the drain. When conveying liquid to the heater bag 22 or to the drain, these tubeε 26/28 can alεo carry air that accumulateε in the upper region of the pump chambers P1/P2. In this arrangement, the heater bag 22, like the drain, serveε as an air sink for the system 10. Valve stations V5 to VIO serve only the lower portε 66(1)/(2) of both pump chamberε Pl and P2. These valve εtationε V5 to VIO, in turn, serve only the primary liquid paths F3; F4; and F5. Branch liquid path F8 links primary paths F3 to F5 with the lower port 66(1) of pump chamber Pl through valve stationε V8; V9; and VIO. Branch liquid path F9 linkε primary pathε F3 to F5 with the lower port 66(2) of pump chamber P2 through valve εtationε V5; V6; and V7. Because the primary paths F3 to F5 are isolated from communication with the upper ports 64 of both pump chambers Pl and P2, they can serve as critical liquid paths. Thus, the tube 34 that conveys liquid directly to the patient's indwelling catheter can be con¬ nected to one of the lower three connectors 31/33/35 (i.e., to the primary liquid paths F3 to F5) . The same tube 34 also carries spent dialysate from the patient's peritoneal cavity. Likewise, the tubes 30/32 that carry sterile source liquid into the pump chambers enter through the lower pump chamber ports 66(1)/ (2). This arrangement makes it unnecessary to incorporate bubble traps and air vents in the tubing serving the cassette. The casεette iε its own self contained air trap. II. THE CYCLER As Figs. 9 and 10 best show, the cycler 14 carrieε the operating elementε eεsential for an APD procedure within a portable housing 82 that occupies a relatively small footprint area (as Figs. 1 and 2 alεo show) . Aε already εtated, the houεing 82 encloεeε the cycle controller 16. The houεing 82 alεo encloεes a bag heater module 74 (see Fig. 9) . It further encloses a pneumatic actuator module 76. The pneumatic actuator module 76 alεo incorporateε the cassette holder 100 already described, as well as a failsafe liquid shutoff asεembly 80, which will be described later. The housing 82 also encloses a source 84 of pneumatic preεsure and an associated pneumatic pressure distribution module 88, which linkε the presεure source 84 with the actuator module 76. The houεing 82 alεo encloseε an AC power supply module 90 and a back-up DC battery power supply module 92 for the cycler 14. Further εtructural and functional details of these operating modules of the cycler 14 will be de¬ scribed next. (A) The Bag Heating Module The bag heating module 74 includes an exterior support plate 94 on the top of the cycler housing 82 for carrying the heater bag 22 (aε Fig. 1 εhowε) . The support plate 94 is made of a heat conducting material, like aluminum. As Fig. 9 shows, the module 74 includeε a conventional electrical resiεtance heating εtrip 96 that underlieε and heatε the support plate 94. Four thermocouples T1/T2/T3/T4 monitor the temperatures at spaced locations on the left, right, rear, and center of the heating εtrip 96. Fifth and sixth thermocouples T5/T6 (see Figs. 2 and 10) independently monitor the temperature of the heater bag 22 itself. A circuit board 98 (see Fig. 9) receives the output of the thermocouples Tl to T6. The board 98 conditions the output before transmitting it to the controller 16 for processing. In the preferred embodiment, the controller 16 includes a heater control algorithm that elevates the temperature of liquid in the heater bag 22 to about 33 degrees C before the first fill cycle. A range of other safe temperature settings could be used, which could be selected by the user. The heating continues as the first fill cycle proceeds until the heater bag temperature reaches 36 degrees C. The heater control algorithm then maintains the bag temperature at about 36 degreeε C. The algorithm functionε to toggle the heating strip 96 on and off at a sensed plate temperature of 44 degrees C to asεure that plate temperature never exceedε 60 degreeε C. (B) The Pneumatic Actuator Module The cassette holder 100, which forms a part of the pneumatic actuator module 76, includes a front plate 105 joined to a back plate 108 (see Fig. 12A) . The plates 105/108 collectively form an interior recess 110. A door 106 is hinged to the front plate 105 (see Figs. 6 and 7) . The door 106 moves between an opened position (shown in Figs. 6 and 7) and a closed position (εhown in Figε. 1; 2; and 11). A door latch 115 operated by a latch handle 111 contacts a latch pin 114 when the door 106 iε closed. Moving the latch handle 111 downward when the door 106 is closed engages the latch 115 to the pin 114 to lock the door 106 (as Figs. 4 and 5 show) . Moving the latch handle 111 upward when the door 106 is closed releaseε the latch 115 from the pin 114. This allows the door 106 to be opened (as Fig. 6 shows) to gain accesε to the holder interior. With the door 106 opened, the user can insert the cassette 24 into the recess 110 with its front side 58 facing the interior of the cycler 14 (aε Figs. 6 and 7 εhow) . The inside of the door 106 carries an upraised elastomeric gaεket 112 poεitioned in oppoεition to the receεε 110. Closing the door 106 brings the gasket 112 into facing contact with the diaphragm 61 on the back εide 60 of the caεsette 24. The pneumatic actuator module 76 contains a pneumatic piston head asεembly 78 located behind the back plate 108 (see Fig. 12A) . The piston head assembly 78 includes a piston element 102. As Figs. 12A; 13 and 14 show, the piston element 102 comprises a molded or machined plastic or metal body. The body containε two pump actuatorε PA1 and PA2 and ten valve actuatorε VA1 to VA10. The pump actuatorε PA1/PA2 and the valve actuatorε VA1 to VA10 are mutually oriented to form a mirror image of the pump stations P1/P2 and valve stations VI to V10 on the front side 58 of the cassette 24. Each actuator PA1/PA2/VA1 to VA10 includes a port 120. The ports 120 convey positive or negative pneumatic pressureε from the pneumatic preεεure diεtribution module 88 (aε will be deεcribed in greater detail later) . As Fig. 13 best showε, interior grooveε 122 formed in the piεton element 102 εurround the pump and valve actuators PA1/PA2/VA1 to VA10. A preformed gasket 118 (see Fig. 12A) fits into these grooves 122. The gasket 118 sealε the peripherieε of the actuators PA1/PA2/VA1 to VA10 againεt pneumatic pressure leakε. The configuration of the preformed gasket 118 follows the pattern of upstanding edges that peripherally surround and separate the pump chambers Pl and P2 and valve stations VI to VIO on the front side 58 of the casεette 24. The piεton element 102 iε attached to a pressure plate 104 within the module 76 (see Fig. 12B) . The pressure plate 104 is, in turn, supported on a frame 126 for movement within the module 76. The side of the plate 104 that carries the piston element 102 abuts against a reεilient spring element 132 in the module 76. In the illustrated and preferred embodiment, the εpring element 132 iε made of an open pore foam material. The frame 126 also supports an inflatable main bladder 128. The inflatable bladder 128 contactε the other side of the plate 104. The piston element 102 extends through a window 134 in the spring element 132 (see Fig. 12A) . The window 134 registerε with the caεεette receiving recess 110. With a cassette 24 fitted into the receεε 110 and the holder door 106 closed, the piston element 102 in the window 134 iε mutually aligned with the diaphragm 59 of the casεette 24 in the holder receεε 110. As Fig. 15A showε, when the main bladder 128 is relaxed (i.e., not inflated), the εpring element 132 contactε the plate 104 to hold the piεton element 102 away from preεεure contact with a cassette 24 within the holder recess 110. As will be described in greater detail later, the pneumatic preεεure diεtribution module 88 can supply positive pneumatic pressure to the main bladder 128. This inflateε the bladder 128. As Fig. 15B showε, when the main bladder 128 inflates, it presεeε the plate 104 against the spring element 132. The open cell structure of the spring element 132 reεiliently deforms under the pressure. The piston element 102 moveε within the window 134 into preεεure contact against the casεette diaphragm 59. The bladder pressure presseε the piεton element gaεket 118 tightly againεt the cassette diaphragm 59. The bladder presεure alεo presses the back side diaphragm 61 tightly against the interior of the door gasket 112. As a result, the diaphragmε 59 and 61 εeat against the upstanding peripheral edges 62 that surround the casεette pump chamberε P1/P2 and valve εtations VI to V10. The pressure applied to the plate 104 by the bladder 128 εealε the peripherieε of these regions of the casεette 24. The piεton element 102 remains in this operating position as long as the main bladder 128 retains poεitive preεεure and the door 106 remainε closed. in this position, the two pump actuators PA1 and PA2 in the piεton element 102 regiεter with the two pump chambers Pl and P2 in the casεette 24. The ten valve actuators VAl to VA10 in the piston element 102 likewise register with the ten valve stationε VI to V10 in the caεsette 24. As will be described in greater detail later, the pneumatic preεεure diεtribution module 88 conveys positive and negative pneumatic fluid pressure to the actuators PA1/PA2/VA1 to VAIO in a sequence governed by the controller 16. These positive and negative preεεure pulεeε flex the dia¬ phragm 59 to operate the pump chamberε P1/P2 and valve stations VI to VIO in the casεette 24. Thiε, in turn, moves liquid through the cassette 24. Venting the positive pressure in the bladder 128 relieves the pressure the plate 104 applies to the caεεette 24. The resilient spring element 132 urges the plate 104 and attached piston element 102 away from presεure contact with the caεεette diaphragm 59. In thiε poεition, the door 106 can be opened to unload the cassette 24 after use. As Fig. 12A shows, the gasket 118 preferably includes an integral elastomeric membrane 124 stretched across it. Thiε membrane 124 iε expoεed in the window 134. It εerveε aε the interface between the piston element 102 and the diaphragm 59 of the caεεette 24, when fitted into the holder recess 110. The membrane 124 includes one or more small through holes 125 in each region overlying the pump and valve actuators PA1/PA2/VA1 to VA10. The holes 125 are sized to convey pneumatic fluid preεεure from the piston element actuators to the casεette diaphragm 59. Nevertheleεε, the holeε 125 are small enough to retard the passage of liquid. This forms a flexible splash guard acrosε the expoεed face of the gaεket 118. The splash guard membrane 124 keeps liquid out of the pump and valve actuators PA1/PA2/VA1 to VA10, should the cassette diaphragm 59 leak. The splaεh guard membrane 124 also εerveε aε a filter to keep particulate matter out of the pump and valve actuators of the piston element 102. The splash guard membrane 124 can be periodically wiped clean when cassettes are exchanged. As Fig. 12A shows, inserts 117 preferably occupy the pump actuators PA1 and PA2 behind the membrane 124. In the illuεtrated and preferred embodiment, the inserts 117 are made of an open cell foam material. The insertε 117 help dampen and direct the pneumatic preεεure upon the membrane 124. The presence of insertε 117 εtabilizes air pressure more quickly within the pump actuators PA1 and PA2, helping to negate transient thermal effects that arise during the conveyance of pneumatic preεεure. (C) The Liquid Shutoff Assembly The liquid shutoff assembly 80, which forms a part of the pneumatic actuator module 76, serves to block all liquid flow through the casεette 24 in the event of a power failure or another designated error condition. As Fig. 12B showε, the liquid shutoff assembly 80 includes a movable occluder body 138 located behind the presεure plate frame 126. The occluder body 138 haε a εide hook element 140 that fits into a slot 142 in the pressure plate frame 126 (see Figs. 16A/B) . Thiε hook-in-slot fit establishes a contact point about which the occluder body 138 pivots on the presεure plate frame 126. The occluder body 138 includeε an elongated occluder blade 144 (εee Figε. 12A; 15; and 16) . The occluder blade 144 extendε through a slot 146 in the front and back plates 105/108 of the holder 100. When the holder door 106 is closed, the blade 144 faces an elongated occluder bar 148 carried on the holder door 106 (see Figs. 15 and 16). When the cassette 24 occupies the holder recess 110 (see Fig. 7) and the holder door 106 is closed, all tubing 26 to 34 attached to the cassette 24 passes between the occluder blade 144 and the occluder bar 148 (as Figs. 15 and 16 εhow) . In the illustrated and preferred embodiment, a region 145 of the flexible tubing 26 to 34 is held in a mutually close relationship near the cassette 24 (see Fig. 3) . This bundled tubing region 145 further simplifies the handling of the cassette 24. This bundled region 145 also arranges the casεette tubing 26 to 34 in a close, side by side relationship in the region between the occluder blade 144 and bar 148 (see Fig. 7) . In the illustrated and preferred embodiment, the sidewalls of the flexible tubing 26 to 34 are RF surface welded together to form the bundled region 145. Pivotal movement of the occluder body 138 moves the. occluder blade 144 toward or away from the occluder bar 148. When spaced apart (as Fig. 16A shows) , the occluder blade and bar 144/148 allow clear passage of the casεette tubing 26 to 34. When brought together (aε Fig. 16B shows) , the occluder blade and bar 144/148 crimp the cassette tubing 26 to 34 closed. Occluder springs 150 carried within sleeveε 151 normally bias the occluder blade and bar 144/148 together. An occluder bladder 152 occupies the space between the occluder body 138 and the frame 126 (see Fig. 12B) . As Fig. 16B shows, when the occluder bladder 152 iε relaxed (i.e., not inflated), it makeε no contact againεt the occluder body 138. The occluder springs 150 urge the occluder blade and bar 144/148 together, simultaneously crimping all cassette tubing 26 to 34 closed. Thiε preventε all liquid flow to and from the cassette 24. As will be described in greater detail later, the pneumatic preεεure diεtribution module 88 can supply positive pneumatic pressure to the occluder bladder 152. This inflates the bladder 128. As Fig. 16A shows, when the occluder bladder 152 inflates, it presεes againεt the occluder body 138 to pivot it upward. Thiε moves the occluder blade 144 away from the occluder bar 158. This permits liquid to flow through all tubing to and from the cassette 24. The occluder blade and bar 144/148 remain spaced apart as long as the occluder bladder 152 re¬ tains positive presεure. Venting of poεitive preεεure relaxeε the occluder bladder 152. The occluder springs 150 immediately urge the occluder blade and bar 144/148 back together to crimp the tubing closed. Aε will be deεcribed in greater detail later, an electrically actuated valve C6 communicateε with the occluder bladder 152. When receiving electrical power, the valve C6 iε normally closed. In the event of a power losε, the valve C6 openε to vent the occluder bladder 152, crimping the caεεette tubing 26 to 34 cloεed. The aεsembly 80 provides a pneumatically actuated fail-safe liquid shut off for the pneumatic pumping system. (D) The Pneumatic Pressure Source The pneumatic preεεure source 84 comprises a linear vacuum pump and air compressor capable of generating both negative and positive air pressure. In the illustrated and preferred embodiment, the pump 84 is a conventional air compressor/vacuum pump commercially available from Medo Corporation. As Fig. 23 shows, the pump 84 includes an inlet 154 for drawing air into the pump 84. The pump inlet 154 supplies the negative pressure required to operate the cycler 14. As Fig. 23 also εhows, the pump 84 also includes an outlet 156 for discharging air from the pump 84. The pump outlet 156 supplies positive preεεure required to operate the cycler 14. Figε. 9 and 10 also show the inlet 154 and outlet 156. The pump inlet 154 and the pump outlet 156 communicate with ambient air via a common vent 158 (shown schematically in Fig. 23) . The vent 158 in- eludes a filter 160 that removes particulateε from the air drawn into the pump 84. (E) The Pressure Distribution System Figε. 17 to 22 show the details of the pneumatic presεure diεtribution module 88. The module 88 encloses a manifold asεembly 162. The manifold aεεembly 162 controlε the diεtribution of poεitive and negative presεureε from the pump 84 to the piεton element 102, the main bladder 128, and the occluder bladder 152. The controller 16 provideε the command εignals that govern the operation of the manifold asεembly 162. Aε Figε. 18 εhowε, a foam material 164 preferably lineε the interior of the module 88 enclosing the manifold asεembly 162. The foam material 164 provides a barrier to dampen sound to assures quiet operation. As Figs. 18 and 19 εhow, the manifold assembly 162 includes a top plate 166 and a bottom plate 168. A sealing gasket 170 is sandwiched between the plates 166/168. The bottom plate 168 (see Figε. 20 and 21) includes an array of paired air ports 172. Fig. 20 shows the inside εurface of the bottom plate 168 that faces the gasket 170 (which iε designated IN in Figs. 19 and 20) . Fig. 21 showε the outside surface of the bottom plate 168 (which is deεignated OUT in Figs. 19 and 21) . The inside surface (IN) of the bottom plate 168 also containε an array of interior grooveε that form air conduction channelε 174 (εee Fig. 20) . The array of paired air portε 172 communicateε with the channelε 174 at εpaced intervals. A block 176 fastened to the outside εurface (OUT) of the bottom plate 168 containε an additional air conduction channelε 174 that communicate with the channelε 174 on the inεide plate surface (IN) (see Figs. 19 and 22) . Transducers 178 mounted on the exterior of the module 88 sense through asεociated senεing tubeε 180 (εee Fig. 18) pneumatic preεεure conditionε present at various points along the air conduction channelε 174. The transducers 178 are conventional semi¬ conductor piezo-resiεtance preεεure sensorε. The top of the module 88 includeε stand-off pins 182 that carry a board 184 to which the pressure transducerε 178 are attached. The outεide εurface (OUT) of the bottom plate 168 (εee Figs. 19 and 22) carries a solenoid actuated pneumatic valves 190 connected in communication with each pair of air ports 172. In the illustrated embodiment, there are two rows of valves 190 arranged along oppoεite sides of the outside surface (OUT) of the plate 168. Twelve valves 190 form one row, and thirteen valveε 190 form the other row. As Fig. 22 showε, each pneumatic valve 190 iε attached in communication with a pair of air portε 172 by screws fastened to the outside surface (OUT) of the bottom plate 168. As Figs. 19 and 22 also show, each valve 190 is electrically connected by ribbon cables 192 to the cycler controller 16 by contacts on a junction board 194. There are two junction boards 194, one for each row of valves 190. Each pneumatic valve 190 operates to control air flow through its associated pair of ports 172 to link the ports 172 to the various air channels 174 the bottom plate 168 carries. As will be deεcribed in greater detail later, some of the valves 190 are conventional three way valves. Others are conventional normally closed two way valves. The air channels 174 within the manifold aεsembly 162 are coupled by flexible tubing 196 (see Fig. 17) to the system components that operate using pneumatic pressure. Slots 198 in the εide of the module 88 accommodate the passage of the tubing 196 connected to the manifold asεembly 162. Figε. 9 and 10 alεo εhow the flexible tubing 196 that linkε the manifold aεsembly 162 to the pneumatically actuated and controlled system components. Fig. 11 further shows the tubing 196 from the manifold assembly 162 entering the pneumatic actuator module 76, where they connect to the main bladder 128, the occluder bladder 152, and the piston element 102. Fig. 14A further showε the T- fittingε that connect the tubing 196 to the portε of the valve actuators VAl to VAIO and the ports of the pump actuators PA1/PA2 of the piston element 102. These connections are made on the back side of the piston element 102. 1. The Pressure Regulation System The air conduction pasεageε 174 and the flexible tubing 196 aεεociated with the manifold assembly 162 define a fluid pressure regulation system 200 that operates in responεe to command signals from the cycler controller 16. Figs. 23 and 24 show the details of the air regulation syεtem 200 in schematic form. In responεe to the command εignalε of the controller 16, the pressure regulation system 200 directs the flow of positive and negative pneumatic presεures to operate the cycler 14. When power is applied, the system 200 maintains the occluder assembly 80 in an open, flow-permitting condition; it seals the cassette 24 within the holder 100 for operation; and it conveys pneumatic pressure to the piεton element 102 to move liquid through the cassette 24 to conduct an APD procedure. The pressure regulation syεtem 200 also provides in¬ formation that the controller 16 processes to measure the volume of liquid conveyed by the caεsette 24. a. Pressure Supply Network As Fig. 23 showε, the regulation system 200 includes a presεure εupply network 202 having a poεitive preεεure εide 204 and a negative preεεure εide 206. The poεitive and negative preεsure sides 204 and 206 can each be selectively operated in either a low-relative pressure mode or high-relative pressure mode. The controller 16 calls for a low-relative pressure mode when the cycler 14 circulates liquid directly through the patient'ε indwelling catheter 18 (i.e., during patient infusion and drain phases). The controller 16 calls for a high-relative pressure mode when the cycler 14 circulates liquid outside the patient's indwelling catheter 18 (i.e., during transfers of liquid from supply bags 20 to the heater bag 22) . In other words, the controller 16 activates the low-relative presεure mode when considerations of patient comfort and safety predominate. The controller 16 activateε the high-relative preεεure mode when conεiderations of processing speed predominate. In either mode, the pump 84 drawε air under negative preεsure from the vent 158 through an inlet line 208. The pump 84 expels air under poεitive pressure through an outlet line 210 to the vent 158. The negative presεure εupply εide 206 commu¬ nicates with the pump inlet line 208 through a nega- tive presεure branch line 212. The three way pneumatic valve DO carried on the manifold assembly 162 controls thiε communication. The branch line 212 supplies negative presεure to a reservoir 214 carried within the cycler housing 82 (this can be seen in Figε. 9 and 10) . The reεervoir 214 preferably has a capacity greater than about 325 cc and a collapse presεure of greater than about -10 pεig. The transducer XNEG carried on the manifold asεembly 162 εenεeε the amount of negative preεεure εtored within the negative pressure reservoir 214. When in the high-relative negative pressure mode, the transducer XNEG transmits a control signal when the predefined high-relative negative presεure of -5.0 psig is sensed. When in the low-relative negative presεure mode, the tranεducer XNEG transmits a control εignal when the predefined low- relative negative pressure of -1.2 psig is sensed. The pressure reservoir 214 serves as both a low- relative and a high-relative pressure reservoir, depending upon the operating mode of the cycler 14. The poεitive preεεure εupply εide 204 commu¬ nicateε with the pump outlet line 210 through a main poεitive presεure branch line 216. The three way pneumatic valve C5 controls this communication. The main branch line 216 supplieε poεitive preεεure to the main bladder 128, which seats the piston head 116 againεt the casεette 24 within the holder 100. The main bladder 128 alεo serves the syεtem 202 as a poεitive high preεεure reεervoir. The main bladder 128 preferably haε a capacity of greater than about 600 cc and a fixtured burεt preεsure over about 15 psig. Transducer XHPOS carried on the manifold assembly 162 senεeε the amount of poεitive preεεure within the main bladder 128. Tranεducer XHPOS transmits a control εignal when the predetermined high-relative preεεure of 7.5 pεig iε εenεed. A firεt auxiliary branch line 218 leadε from the main branch line 216 to a εecond positive presεure reεervoir 220 carried within the houεing 82 (which can also be seen in Figε. 9 and 10) . The two way, normally cloεed pneumatic valve A6 carried by the manifold asεembly 168 controlε the paεsage of positive pressure to the second reservoir 220. The second reservoir 220 εerveε the εyεtem 202 aε a reservoir for low-relative positive pressure. The second reservoir 220 preferably has a capacity of greater than about 325 cc and a fixtured burst presεure greater than about 10 pεig. Transducer XLPOS carried on the manifold assembly 162 senses the amount of positive pressure within the second pressure reservoir 220. Transducer XLPOS is set to transmit a control signal when the predetermined low-relative pressure of 2.0 psig is sensed. The valve A6 divides the poεitive preεεure εupply εide 204 into a high-relative poεitive preεεure region 222 (between valve εtation C5 and valve station A6) and a low-relative positive pressure region 224 (between valve station A6 and the second reservoir 220) . A second auxiliary positive presεure branch line 226 leads from the main branch line 216 to the occluder bladder 152 through three way pneumatic valve C6. The occluder bladder 152 also serveε the εyεtem 202 as a positive high presεure reservoir. A bypasε branch line 228 leadε from the main branch 216 to the vent 158 through the two way, nor- mally cloεed valve A5. The valve C6 also communicates with the bypaεε branch line 228. The pressure supply network 202 has three modes of operation. In the first mode, the network 202 supplies the negative presεure εide 206. In the εecond mode, the network 202 supplies the positive pressure side 204. In the third mode, the network 202 supplies neither negative or positive pressure side 204/206, but serveε to circulate air in a continuouε manner through the vent 158. With the three modeε of operation, the pump 84 can be continuouεly operated, if deεired. Thiε avoidε any time delayε and noiεe occaεioned by cycling the pump 84 on and off. In the firεt mode, valve εtation DO openε communication between the negative branch line 212 and the pump inlet line 208. Valve C5 opens communication between the pump outline line 210 and the vent 158, while blocking communication with the main positive branch line 216. The pump 84 operates to circulate air from the vent 158 through its inlet and outlet lines 208/210 to the vent 158. This circulation also draws air to generating negative pressure in the negative branch line 212. The reservoir 214 εtoreε thiε negative preεεure. When the tranεducer XNEG senses its prede¬ termined high-relative or low-relative negative preεεure, it εupplies a command signal to operate valve DO, cloεing communication between the pump inlet line 208 and the negative branch line 212. In the εecond mode, valve DO cloεeε communi¬ cation between the negative branch line 212 and the pump inlet line 208. Valve C5 closeε communication with the vent 158, while opening communication with the main poεitive branch line 216. The pump 84 operates to convey air under positive pressure into the main positive branch line 216. Thiε poεitive preεεure accumulateε in the main bladder 128 for conveyance to the pump and valve actuatorε on the piεton element 102. By operating three way valve C6, the poεitive preεεure can alεo be directed to fill the occluder bladder 152. When the valve C6 iε in this position, the positive presεure in the occluder bladder 152 alεo can be conveyed to the pump and valve actuators on the piston element 102 Otherwise, valve C6 directs the positive pressure through the bypass line 228 to the vent 158. In the absence of an electrical signal (for example, if there iε a power failure) , valve C6 opens the occluder bladder 152 to the bypasε line 228 to the vent 158. Valve A6 is either opened to convey air in the main branch line 216 to the low pressure reservoir 214 or closed to block this conveyance. The transducer XLPOS opens the valve A6 upon sensing a pressure below the low-relative cut-off. The tranεducer XLPOS cloεeε the valve εtation A6 upon εenεing preεεure above the low-relative cut-off. The tranεducer XHIPOS operateε valve C5 to close communication between the pump outlet line 210 and the main positive branch line 216 upon sensing a pressure above the high-relative cut-off of 7.5 psig. In the third mode, valve DO closes communi¬ cation between the negative branch line 212 and the pump inlet line 208. Valve C5 opens communication between the pump outlet line 210 and the vent 158, while blocking communication with the main poεitive branch line 216. The pump 84 operates to circulate air in a loop from the vent 158 through itε inlet and outlet lines 208/210 back to the vent 158. b. The Pressure Actuating Network Aε Fig. 24 showε, the regulation system also includes first and second preεεure actuating networkε 230 and 232. The firεt preεεure actuating network 230 diεtributes negative and positive pressures to the firεt pump actuator PA1 and the valve actuatorε that serve it (namely, VAl; VA2; VA8; VA9; and VAIO). These actuatorε, in turn, operate caεsette pump station Pl and valve stationε VI; V2; V8; V9; and VIO, respectively, which serve pump station Pl. The second presεure actuating network 232 diεtributeε negative and poεitive preεεureε to the εecond pump actuator PA2 and the valve actuatorε that serve it (namely, VA3; VA4; VA5; VA6; and VA7) . These actuators, in turn, operate casεette pump station P2 and caεεette valve εtations V3; V4; V5; V6; and V7, which serve pump εtation P2. The controller 16 can operate the firεt and second actuating networks 230 and 232 in tandem to alternately fill and empty the pump chambers Pl and P2. This provideε virtually continuouε pumping action through the caεεette 24 from the εame source to the same destination. Alternatively, the controller 16 can operate the first and second actuating networks 230 and 232 independently. In this way, the controller 16 can provide virtually simultaneous pumping action through the casεette 24 between different εourceε and different destinationε. Thiε εimultaneouε pumping action can be conducted with either εynchronouε or non-εynchronouε pressure delivery by the two networks 230 and 232. The networks 230 and 232 can alεo be operated to provide preεεure delivery that driftε into an out of εynchronouεneεε. The firεt actuating network 230 provideε high- relative poεitive preεεure and negative pressures to the valve actuators VAl; VA2; VA8; VA9; and VA10. The first actuating network 230 also εelec- tively provideε either high-relative poεitive and negative preεsure or low-relative poεitive and negative preεsure to the first pumping actuator PA1. Referring first to the valve actuators, three way valves CO; Cl; C2; C3; and C4 in the manifold assembly 162 control the flow of high-relative positive pressure and negative pressures to the valve actuators VAl; VA2; VA8; VA9; and VAIO. The high-relative positive pressure region of the main branch line 216 communicates with the valves CO; Cl: C2; C3; and C4 through a bridge line 234, a feeder line 236, and individual connecting lines 238. The negative pressure branch 212 communicates with the valves CO; Cl; C2; C3; and C4 through individual connecting lines 340. The controller 16 εetε this branch 212 to a high-relative negative pressure condition by setting the transducer XNEG to sense a high-relative pressure cut-off. By applying negative preεsure to one or more given valve actuators, the associated cassette valve station is opened to accommodate liquid flow. By applying positive presεure to one or more given valve actuators, the asεociated caεεette value εtation iε closed to block liquid flow. In this way, the desired liquid path leading to and from the pump chamber Pl can be selected. Referring now to the pump actuator PA1, two way valve A4 in the manifold aεεembly 162 communicates with the high-relative preεsure feeder line 236 through connecting line 342. Two way valve A3 in the manifold asεembly 162 communicateε with the low- relative positive presεure reεervoir through connecting line 344. By εelectively operating either valve A4 or A3, either high-relative or low- relative positive pressure can be supplied to the pump actuator PAl. Two way valve AO communicateε with the negative pressure branch 212 through connecting line 346. By setting the transducer XNEG to εenεe either a low- relative preεεure cut-off or a high-relative pressure cut-off, either low-relative or high- relative pressure can be supplied to the pump actuator VAl by operation of valve AO. By applying negative preεsure (through valve AO) to the pump actuator PAl, the casεette diaphragm 59 flexes out to draw liquid into the pump chamber Pl. By applying positive presεure (through either valve A3 or A4) to the pump actuator PAl, the cassette diaphragm 59 flexes in to pump liquid from the pump chamber Pl (provided, of course, that the associated inlet and outlet valves are opened) . By modulating the time period during which presεure iε applied, the pumping force can be modulated between full strokes and partial strokeε with reεpect to the pump chamber Pl. The second actuating network 232 operates like the firεt actuating network 230, except it serveε the second pump actuator PA2 and its asεociated valve actuatorε VA3 ; VA4 ; VA5; VA6; and VA7. Like the firεt actuating network 230, the second actuating network 232 provides high-relative positive presεure and high-relative negative preεsures to the valve actuatorε VA3 ; VA4; VA5; VA6; and VA7. Three way valveε Dl; D2: D3 ; D4 ; and D5 in the manifold aεsembly 162 control the flow of high- relative positive pressure and high-relative negative presεureε to the valve actuatorε VA3 ; VA4 ; VA5; VA6; and VA7. The high-relative poεitive preεεure region 222 of the main branch line communicateε with the valveε Dl; D2; D3; D4; and D5 through the bridge line 234, the feeder line 236, and connecting lineε 238. The negative preεεure branch 212 communicateε with the valves Dl: D2; D3; D4; and D5 through connecting lineε 340. This branch 212 can be set to a high-relative negative pressure condition by setting the transducer XNEG to senεe a high-relative pressure cut-off. Like the first actuating network 230, the second actuating network 232 εelectively provideε either high-relative poεitive and negative pressure or low-relative positive and negative pressure to the second pumping actuator PA2. Two way valve BO in the manifold asεembly 162 communicateε with the high-relative pressure feeder line through connecting line 348. Two way valve station Bl in the manifold assembly 162 communicates with the low- relative positive presεure reεervoir through connecting line 349. By selectively operating either valve B0 or Bl, either high-relative or low- relative poεitive preεεure can be εupplied to the pump actuator PA2. Two way valve B4 communicateε with the negative pressure branch through connecting line 350. By setting the tranεducer XNEG to εenεe either a low- relative preεεure cut-off or a high-relative preεεure cut-off, either low-relative or high- relative pressure can be supplied to the pump actuator PA2 by operation of valve B4. Like the first actuating network 230, by applying negative presεure to one or more given valve actuatorε, the aεεociated caεεette value εtation iε opened to accommodate liquid flow. By applying poεitive preεεure to one or more given valve actuatorε, the associated cassette value εtation is closed to block liquid flow. In this way, the desired liquid path leading to and from the pump chamber P2 can be selected. By applying a negative pressure (through valve B4) to the pump actuator PA2, the casεette diaphragm flexes out to draw liquid into the pump chamber P2. By applying a positive presεure (through either valve BBO or Bl) to the pump actuator PA2, the caε¬ εette diaphragm flexeε in to move liquid from the pump chamber P2 (provided, of course, that the asεociated inlet and outlet valves are opened) . By modulating the time period during which pressure is applied, the pumping force can be modulated between full strokes and partial strokeε with reεpect to the pump chamber P2. The first and second actuating networks 230/232 can operate in succeεεion, one drawing liquid into pump chamber Pl while the other pump chamber P2 puεheε liquid out of pump chamber P2, or vice verεa, to move liquid virtually continuouεly from the εame εource to the same deεtination. The firεt and εecond actuating networkε 230/232 can alεo operate to simultaneously move one liquid through pump chamber Pl while moving another liquid through pump chamber P2. The pump chambers Pl and P2 and serve the same or different destinationε. Furthermore, with additional reεervoirε, the firεt and εecond actuation networkε 232/232 can operate on the εame or different relative preεεure conditionε. The pump chamber Pl can be operated with low-relative poεitive and negative pressure, while the other pump chamber P2 is operated with high-relative positive and negative pressure. c. Liguid Volume Measurement As Fig. 24 shows, the presεure regulating syεtem 200 also includes a network 350 that works in conjunction with the controller 16 for measuring the liquid volumes pumped through the casεette. The liquid volume meaεurement network 350 includes a reference chamber of known air volume (V s ) associated with each actuating network. Reference chamber VS1 is associated with the first actuating network. Reference chamber VS2 iε aεεociated with the second actuating network. The reference chambers VS1 and VS2 may be incorporated at part of the manifold aεsembly 162, as Fig. 20 shows. In a preferred arrangement (as Fig. 14B shows) , the reference chamberε VS1 and VS2 are carried by the piston element 102' itself, or at another located close to the pump actuators PAl and PA2 within the casεette holder 100. In thiε way, the reference chamberε VS1 and VS2, like the pump actuators PAl and PA2, exposed to generally the εame temperature conditionε aε the caεεette itεelf. Alεo in the illustrated and preferred embodiment, inserts 117 occupy the reference chambers VS1 and VS2. Like the inserts 117 carried within the pump actuators PAl and PA2, the reference chamber inεertε 117 are made of an open cell foam material. By dampening and directing the application of pneumatic preεεure, the reference chamber inserts 117 make measurement of air volumes faster and lesε complicated. Preferably, the inεert 117 alεo includeε a heat conducting coating or material to help conduct heat into the reference chamber VS1 and VS2. In the illustrated embodiment, a thermal paste is applied to the foam inεert. Thiε preferred arrangement minimizeε the effects of temperature differentials upon liquid volume measurements. Reference chamber VS1 communicates with the outletε of valveε AO; A3: and A4 through a normally closed two way valve A2 in the manifold assembly 162. Reference chamber VS1 also communicates with a vent 352 through a normally closed two way valve Al in the manifold asεembly 162. Tranεducer XVS1 in the manifold aεsembly 162 senεeε the amount of air preεεure preεent within the reference chamber VS1. Transducer XP1 senseε the amount of air preεsure preεent in the first pump actuator PAl. Likewise, reference chamber VS2 communicates with the outlets of valve BO; Bl; and B4 through a normally closed two way valve B2 in the manifold asεembly 162. Reference chamber VS2 alεo communicateε with a filtered vent 356 through a normally cloεed two way valve B3 in the manifold aεsembly 162. Transducer XVS2 in the manifold assembly 162 senses the amount of air presεure preεent within the reference chamber VS2. Tranεducer XP2 senses the amount of air pressure present in the εecond pump actuator PA2. The controller 16 operateε the network 350 to perform an air volume calculation twice, once during each draw (negative preεεure) cycle and once again during each pump (poεitive preεεure) cycle of each pump actuator PAl and PA2. The controller 16 operateε the network 350 to perform the first air volume calculation after the operating pump chamber iε filled with the liquid to be pumped (i.e., after its draw cycle). This provides an initial air volume (V j ) . The controller 16 operateε the network 350 to perform the second air volume calculation after moving fluid out of the pump chamber (i.e., after the pump cycle) . Thiε provideε a final air volume (V f ). The controller 16 calculates the difference between the initial air volume V j and the final air volume Vf to derive a delivered liquid volume (V d ) , where: V d = V f - V j The controller 16 accumulates V^ for each pump chamber to derive total liquid volume pumped during a given procedure. The controller 16 also applies the incremental liquid volume pumped over time to derive flow rates. The controller 16 derives V j in thiε way (pump chamber Pl iε uεed aε an example) : (1) The controller 16 actuateε the valveε CO to C4 to close the inlet and outlet pasεages leading to the pump chamber Pl (which iε filled with liquid) . Valveε A2 and Al are normally closed, and they are kept that way. (2) The controller 16 opens valve Al to vent reference chamber VS1 to atmosphere. The controller 16 then conveys poεitive presεure to the pump actuator PAl, by opening either valve A3 (low- reference) or A4 (high-reference) , depending upon the preεsure mode selected for the pump stroke. (3) The controller 16 closeε the vent valve Al and the poεitive preεεure valve A3 or A4, to iεolate the pump chamber PAl and the reference chamber VS1. (4) The controller 16 meaεureε the air pressure in the pump actuator PAl (using transducer XP1) ( P jj i) and the air pressure in the reference chamber VSl (using transducer XVS1) (IP s ι) • (5) The controller 16 openε valve A2 to allow the reference chamber VSl to equilibrate with the pump chamber PAl. (6) The controller 16 measures the new air pressure in the pump actuator PAl (uεing tranεducer XPl) (IP d 2) and the new air preεεure in the reference chamber (uεing transducer XVS1) (IP S 2) • (7) The controller 16 closes the positive presεure valve A3 or A4. (8) The controller 16 calculateε initial air volume V j aε followε: After the pump chamber Pl iε emptied of liquid, the same sequence of measurementε and calculations are made to derive Vf, as follows: (9) Keeping valve stations A2 and Al closed, the controller 16 actuates the valves CO to C4 to close the inlet and outlet passageε leading to the pump chamber Pl (which iε now emptied of liquid) . (10) The controller 16 openε valve Al to vent reference chamber VSl to atmoεphere, and then conveyε poεitive pressure to the pump actuator PAl, by opening either valve A3 (low-reference) or A4 (high-reference) , depending upon the pressure mode selected for the pump stroke. (11) The controller 16 closeε the vent valve Al and the poεitive preεsure valve A3 or A4 , to isolate the pump actuator PAl and the reference chamber VSl . (12) The controller 16 measures the air pressure in the pump actuator PAl (using transducer XP1) (FP dJ ) and the air pressure in the reference chamber VSl (using tranεducer XVS1) (FP sl ) . (13) The controller 16 openε valve A2 , allowing the reference chamber VSl to equilibrate with the pump actuator. (14) The controller 16 meaεures the new air pressure in the pump actuator PAl (using transducer XP1) (FP d2 ) and the new air pressure in the reference chamber (using transducer XVS1) (FP s2 ) • (15) The controller 16 closes the positive pressure valve A3 or A4. (16) The controller 16 calculates final air volume Vf as followε: V f = __lFP sl ^_FP s2 l_*_V s _ ( FP d2 " FP dl) The liquid volume delivered (V d ) during the preceding pump stroke iε: V d = V f - V; Preferably, before beginning another pump stroke, the operative pump actuator is vented to atmosphere (by actuating valveε A2 and Al for pump actuator PAl, and by actuating valveε B2 and B3 for pump actuator PA2) . The controller 16 alεo monitorε the variation of V d over time to detect the preεence of air in the cassette pump chamber P1/P2. Air occupying the pump chamber P1/P2 reduces the capacity of the chamber to move liquid. If V d decrease over time, or if V d falls below a set expected value, the controller 16 attributes- this condition to the buildup of air in the cassette chamber. When this condition occurs, the controller 16 conducts an air removal cycle, in which liquid flow through the affected chamber is channeled through the top portion of the chamber to the drain or to the heater bag for a period of time. The air removal cycle rids the chamber of excesε air and reεtores V d to expected values. In another embodiment, the controller 16 periodically conducts an air detection cycle. In this cycle, the controller 16 delivers fluid into a given one of the pump chambers Pl and P2. The controller 16 then cloεeε all valve stations leading into and out of the given pump chamber, to thereby trap the liquid within the pump chamber. The controller 16 then applies air preεεure to the actuator aεεociated with the pump chamber and deriveε a series of air volume V j measurementε over a period of time in the manner previouεly diεcloεed. Since the liquid trapped within the pump chamber iε relatively incompreεsible, there should be virtually no variation in the measured V j during the time period, unleεε there iε air present in the pump chamber. If V; does vary over a prescribed amount during the time period, the controller 16 contributes this to the presence of air in the pump chamber. When this condition occurs, the controller 16 conducts an air removal cycle in the manner previously described. The controller 16 perfor ε the liquid volume calculationε assuming that the temperature of the reference chamber VS1/VS2 does not differ significantly from the temperature of the pump chamber P1/P2. One way to minimize any temperature difference iε to mount the reference chamber as close to the pump chamber as poεεible. Fig. 14B shows this preferred alternative, where the reference chamber is physically mounted on the piston head 116. Temperature differences can also be accounted for by applying a temperature correction factor (F t ) to the known air volume of the reference chamber V s to derive a temperature-corrected reference air volume V st , as followε: where: and where: C t is the absolute temperature of the caεsette (expressed in degrees Rankine or Kelvin) , and ^ is the temperature of the reference chamber (expressed in the same units as C t ) . In thiε embodiment, the network εubstitutes V st for V s in the above volume derivation calculationε. The value of F t can be computed baεed upon actual, real time temperature calculationε uεing temperature sensors associated with the casεette and the reference chamber. Because liquid volume measurementε are derived after each pumping stroke, the same accuracy iε obtained for each cassette loaded into the cycler, regardlesε of variationε in tolerances that may exiεt among the caεsetteε uεed. III. THE CYCLER CONTROLLER 16 Figs. 9; 10; 17; and 18 εhow the cycler controller 16. The controller 16 carries out procesε control and monitoring functions for the cycler 14. The controller 16 includes a user interface 367 with a display screen 370 and keypad 368. The user interface 367 receiveε characterε from the keypad 368, displays text to a display screen 370, and soundε the speaker 372 (shown in Figs. 9 and 10). The interface 367 presents εtatuε information to the uεer during a therapy εeεεion. The interface 367 also allows the user to enter and edit therapy parameters, and to issue therapy commands. In the illustrated embodiment, the controller 16 compriseε a central microproceεεing unit (CPU) 358. The CPU iε etched on the board 184 carried on εtand off pinε 182 atop the εecond module 88. Power harneεεeε 360 link the CPU 358 to the power εupply 90 and to the operative elementε of the manifold aεεembly 162. The CPU 358 employε conventional real-time multi-taεking to allocate CPU cycleε to application tasks. A periodic timer interrupt (for example, every 10 milliseconds) preempts the executing task and schedules another that is in a ready state for execution. If a reschedule is requested, the higheεt priority taεk in the ready εtate iε εcheduled. Otherwise, the next taεk on the liεt in the ready state is scheduled. The following provideε an overview of the operation of the cycler 14 under the direction of the controller CPU 358. (A) The user Interface 1. System Power Up/MAIN MENU (Fig. 25) When power is turned on, the controller 16 runs through an INITIALIZATION ROUTINE. During the initialization routine, the controller 16 verifies that its CPU 358 and associated hardware are working. If these power-up tests fail, the controller 16 enters a shutdown mode. If the power-up testε succeed, the controller 16 loads the therapy and cycle settings saved in non-volatile RAM during the last power-down. The controller 16 runs a comparison to determine whether theεe settings, aε loaded, are corrupt. If the therapy and cycle settings loaded from RAM are not corrupt, the controller 16 prompts the user to presε the GO key to begin a therapy εeεεion. When the uεer preεεeε the GO key, the controller 16 displays the MAIN MENU. The MAIN MENU allowε the uεer to choose to (a) εelect the therapy and adjuεt the aεεociated cycle εettingε; (b) review the ultrafiltrate figureε from the last therapy session, and (c) start the therapy sesεion based upon the current settingε. 2. THERAPY SELECTION MENU (Fig. 26) With choice (a) of the MAIN MENU selected, the controller 16 displays the THERAPY SELECTION MENU. This menu allowε the user to specify the APD modality desired, εelecting from CCPD, IPD, and TPD (with an without full drain phaεeε) . The user can also select an ADJUST CYCLE SUBMENU. This submenu allows the user to select and change the therapy parameters. For CCPD and IPD modalities, the therapy parameters include the THERAPY VOLUME, which iε the total dialyεate volume to be infuεed during the therapy εeεεion (in ml) ; the THERAPY TIME, which is the total time allotted for the therapy (in hours and minutes) ; the FILL VOLUME, which is the volume to be infused during each fill phase (in ml) , based upon the size of the patient's peritoneal cavity; the LAST FILL VOLUME, which iε the final volume to be left in the patient at the end of the εeεεion (in ml) ; and SAME DEXTROSE (Y OR N) , which allowε the user to specify a different dextrose concentration for the laεt fill volume. For the TPD modality, the therapy parameterε include THERAPY VOLUME, THERAPY TIME, LAST FILL VOLUME, AND SAME DEXTROSE (Y OR N) , aε above described. In TPD, the FILL VOLUME parameter is the initial tidal fill volume (in ml) . TPD includes also includes aε additional parameterε TIDAL VOLUME PERCENTAGE, which is the fill volume to be infused and drained periodically, expresεed as a. percentage of the total therapy volume; TIDAL FULL DRAINS, which iε the number of full drainε in the therapy session; and TOTAL UF, which is the total ultrafiltrate expected from the patient during the session (in ml) , based upon prior patient monitoring. The controller 16 includes a THERAPY LIMIT TABLE. This Table setε predetermined maximum and minimum limits and permitted increments for the therapy parameters in the ADJUST CYCLE SUBMENU. The controller 16 also includeε a THERAPY VALUE VERIFICATION ROUTINE. Thiε routine checkε the parameterε selected to verify that a reasonable therapy seεεion haε been programmed. The THERAPY VALUE VERIFICATION ROUTINE checks to aεεure that the selected therapy parameters include a dwell time of at least one minute; at least one cycle; and for TPD the expected filtrate iε not unreasonably large (i.e., it iε less than 25% of the selected THERAPY VOLUME) . If any of these parameters is unreasonable, the THERAPY VALUE VERIFICATION ROUTINE places the user back in the ADJUST CYCLE SUBMENU and identifies the therapy parameter that is most likely to be wrong. The user is required to program a reasonable therapy before leaving the ADJUST CYCLE SUBMENU and begin a therapy sesεion. Once the modality is selected and verified, the controller 16 returns to uεer to the MAIN MENU. 3. REVIEW ULTRAFILTRATION MENU With choice (b) of the MAIN MENU selected, the controller 16 displays the REVIEW ULTRAFILTRATION MENU (see Fig. 25) . This Menu displayε LAST UF, which is the total volume of ultrafiltrate generated by the pervious therapy session. For CCPD and IPD modalities, the user can also select to ULTRAFILTRATION REPORT. This Report provides a cycle by cycle breakdown of the ultrafiltrate obtained from the previous therapy sesεion. 4. SET-UP PROMPTS/LEAK TESTING With choice (c) of the MAIN MENU εelected, the controller 16 first displayε SET-UP PROMPTS to the user (as shown in Fig. 27) . The SET-UP PROMPTS first inεtruct the uεer to LOAD SET. The user is required to open the door; load a caεεette; cloεe the door; and preεε GO to continue with the set-up dialogue. When the user presses GO, the controller 16 pressurizes the main bladder and occluder bladder and tests the door seal. If the door seal fails, the controller 16 promptε the user to try again. If the door continues to fail a predetermined period of times, the controller 16 raises a SYSTEM ERROR and shuts down. If the door seal is made, the SET-UP PROMPTS next instruct the user to CONNECT BAGS. The user is required to connect the bagε required for the therapy session; to unclamp the liquid tubing lines being use and assure that the liquid lines that are not remained clamped (for example, the selected therapy may not require final fill bags, so liquid lines to theεe bagε εhould remain clamped) . Once the user accomplisheε theεe taεkε, he/εhe presses GO to continue with the set-up dialogue. When GO is presεed, the controller 16 checkε which lineε are clamped and uεeε the programmed therapy parameterε to determine which lines should be primed. The controller 16 primes the appropriate lines. Priming removes air from the set lineε by delivering air and liquid from each bag uεed to the drain. Next, the controller 16 performs a predetermined series of integrity tests to assure that no valves in the cassette leak; that there are no leaks between pump chambers; and that the occluder assembly stops all liquid flow. The integrity testε firεt convey the predetermined high-relative negative air preεsure (- 5.0 psig) to the valve actuatorε VAl to VAIO. The tranεducer XNEG monitorε the change in high-relative negative air preεεure for a predetermined period. If the preεεure change over the period exceeds a predetermined maximum, the controller 16 raises a SYSTEM ERROR and shutε down. Otherwiεe, the integrity tests convey the predetermined high-relative positive preεεure (7.0 psig) to the valve actuators VAl to VAIO. The transducer XHPOS monitors the change in high- relative positive air pressure for a predetermined period. If the presεure change over the period exceeds a predetermined maximum, the controller 16 raises a SYSTEM ERROR and shuts down. Otherwise, the integrity testε proceed. The valve actuators VAl to VAIO convey positive pressure to close the cassette valve stationε VI to VIO. The tests first convey the predetermined maximum high- relative negative pressure to pump actuator PAl, while conveying the predetermined maximum high- relative positive pressure to pump actuator PA2. The transducers XP1 and XP2 monitor the pressures in the respective pump actuators PAl and PA2 for a predetermined period. If presεure changes over the period exceed a predetermined maximum, the controller 16 raiseε a SYSTEM ERROR and shuts down. Otherwise, the tests next convey the predetermined maximum high-relative positive pressure to pump actuator PAl, while conveying the predetermined maximum high-relative negative pressure to pump actuator PA2. The transducers XPl and XP2 monitor the pressureε in the reεpective pump actuators PAl and PA2 for a predetermined period. If pressure changes over the period exceed a predetermined maximum, the controller 16 raises a SYSTEM ERROR and shuts down. Otherwise, power to valve C6 is interrupted. Thiε ventε the occluder bladder 152 and urges the occluder blade and plate 144/148 together, crimping casεette tubing 26 to 34 closed. The pump chambers Pl and P2 are operated at the predetermined maximum pressure conditions and liquid volume measurementε taken in the manner previouεly deεcribed. If either pump chamber P1/P2 moveε liquid paεε the closed occluder blade and plate 144/148, the controller 16 raises a SYSTEM ERROR and shuts down. If all integrity testε εucceed, the SET-UP PROMPTS next instruct the user to CONNECT PATIENT. The user is required to connect the patient according to the operator manual and press GO to begin the dialysis therapy session selected. The controller 16 beginε the εesεion and diεplayε the RUN TIME MENU. 5. RUN TIME MENU Attention iε now directed to Fig. 28. The RUN TIME MENU iε the active therapy interface. The RUN TIME MENU provideε an updated real-time status report of the current progresε of the therapy sesεion. The RUN TIME MENU includeε the CYCLE STATUS, which identifieε the total number of fill/dwell/drain phases to be conducted and the present number of the phase underway (e.g., Fill 3 of 10) ; the PHASE STATUS, which diεplayε the preεent fill volume, counting up from 0 ml; the ULTRAFILTRATION STATUS, which diεplayε total ultrafiltrate accumulated εince the εtart of the therapy sesεion; the TIME, which iε the preεent time; and FINISH TIME, which is the time that the therapy sesεion iε expected to end. Preferably, the user can also select in the RUN TIME MENU an ULTRAFILTRATION STATUS REVIEW SUBMENU, which displays a cycle by cycle breakdown of ultrafiltration accumulated. From the RUN TIME MENU, the user can alεo select to STOP. The controller 16 interrupts the therapy session and displays the STOP SUBMENU. The STOP SUBMENU allows the user to REVIEW the programmed therapy parameterε and make change to the parameters; to END the therapy sesεion; to CONTINUE the therapy session; to BYPASS the present phase; to conduct a MANUAL DRAIN; or ADJUST the intensity of the display and loudness of alarmε. REVIEW reεtricts the type of changes that the user can make to the programmed parameters. For example, in REVIEW, the user cannot adjust parameters above or below a maximum specified amounts. CONTINUE returns the user to the RUN TIME MENU and continue the therapy sesεion where it left off. The controller 16 preferably also includes specified time-outs for the STOP SUBMENU. For example, if the user does not take any action in the STOP SUBMENU for 30 minutes, the controller 16 automatically executes CONTINUE to return to the RUN TIME MENU and continue the therapy εeεsion. If the user does not take any action for 2 minuteε after selecting REVIEW, the controller 16 also automatically executes CONTINUE. 6. Background Monitoring Routine/System Errors The controller 16 includes a BACKGROUND MONITORING ROUTINE that verifies system integrity at a predetermined intervals during the therapy seεεion (e.g., every 10 seconds) (as Fig. 29 shows). The BACKGROUND MONITORING ROUTINE includes BAG OVER TEMP, which verifies that the heater bag is not too hot (e.g., not over 44 degreeε c); DELIVERY UNDER TEMP, which verifieε that the liquid delivered to the patient is not too cold (e.g, less than 33 degrees C) ; DELIVERY OVER TEMP, which verifies that the liquid delivered to the patient is not too hot (e.g, over 38 degrees C) ; MONITOR TANKS, which verifieε that the air tankε are at their operating preεεureε (e.g., poεitive tank pressure at 7.5 psi +/- 0.7 psi; patient tank at 5.0 psi +/- 0.7 psi, except for heater to patient line, which iε 1.5 psi +/- 0.2 psi; negative tank pressure at -5.0 psi +/- 0.7psi, except for patient to drain line, which is at -0.8 psi +/- 0.2 psi) ; CHECK VOLTAGES, which verify that power supplies are within their noise and tolerance specs; VOLUME CALC, which yerifieε the volume calculation math; and CHECK CPU, checkε the processor and RAM. When the BACKGROUND MONITORING ROUTINE senses an error, the controller 16 raiseε a SYSTEM ERROR. Loεε of power also raiseε a SYSTEM ERROR. When SYSTEM ERROR occurs, the controller 16 sounds an audible alarm and displayε a message informing the user about the problem senεed. When SYSTEM ERROR occurε, the controller 16 alεo shuts down the cycler 14. During shut down, the controller 16 ensures that all liquid delivery is stopped, activates the occluder asεembly, closes all liquid and air valves, turns the heater plate elementε off. If . SYSTEM ERROR occurε due to power failure, the controller 16 alεo vents the emergency bladder, releasing the door. 7. SELF-DIAGNOSTICS AND TROUBLE SHOOTING According to the invention, the controller 16 monitorε and controls pneumatic pressure within the internal pressure distribution εyεtem 86. Baεed upon pneumatic pressure measurements, the controller 16 calculates the amount and flow rate of liquid moved. The controller does not require an additional external sensing devices to perform any of its control or measurement functions. As a reεult, the system 10 requires no external pressure, weight, or flow sensors for the tubing 26 to 34 or the bags 20/22 to monitor and diagnose liquid flow conditions. The same air pressure that moves liquid through the system 10 also serves to sense and diagnose all relevant external conditions affecting liquid flow, like an empty bag condition, a full bag condition, and an occluded line condition. Moreover, strictly by monitoring the pneumatic pressure, the controller 16 is able to distinguish a flow problem emanating from a liquid source from a flow problem emanating from a liquid destination. Based upon the liquid volume measurementε derived by the meaεurement network 350, the controller 16 alεo deriveε liquid flow rate. Based upon values and changes in derived liquid flow rate, the controller 16 can detect an occluded liquid flow condition. Furthermore, based upon derived liquid flow rates, the controller can diagnose and determine the cause of the occluded liquid flow condition. The definition of an "occluded flow" condition can vary depending upon the APD phaεe being performed. For example, in a fill phase, an occluded flow condition can represent a flow rate of leεε than 20 ml/min. In a drain phase, the occluded flow condition can represent a flow rate of leεs than 10 ml/min. In a bag to bag liquid tranεfer operation, an occluded flow condition can repreεent a flow rate of leεε than 25 ml/min. Occluded flow conditions for pediatric APD sessions can be placed at lower set points. When the controller 16 detects an occluded flow condition, it implements the following heuriεtic to determine whether the occluεion is attributable to a given liquid source or a given liquid destination. When the controller 16 determines that the cassette cannot draw liquid from a given liquid source above the occluded flow rate, the controller 16 determines whether the cassette can move liquid toward the source above the occluded flow rate (i.e., it determines whether the liquid source can serve as a liquid destination) . If it can, the controller 16 diagnoseε the condition aε an empty liquid εource condition. When the controller 16 determineε that the caεεette cannot push liquid toward a given destination above the occluded flow rate, it determineε whether the cassette can draw liquid from the destination above the occluded flow rate (i.e., it determines whether the liquid destination can serve as a liquid source) . If it can, the controller diagnoses the condition as being a full liquid destination condition. When the controller 16 determines that the caεεette can neither draw or puεh liquid to or from a given εource or deεtination above the occluded flow rate, the controller 16 interpretε the condition aε an occluded line between the cassette and the particular source or destination. In this way, the syεtem 10 operateε by controlling pneumatic fluid preεεure, but not by reacting to external fluid or liquid pressure or flow sensing. 8. ALARMS With no SYSTEM ERRORS, the therapy sesεion automatically continues unless the controller 16 raises an ALARM1 or ALARM2. Fig. 30 shows the ALARM1 and ALARM2 routines. The controller 16 raiseε ALARM1 in εituationε that require uεer intervention to correct. The controller 16 raiseε ALARM1 when the controller 16 senses no supply liquid; or when the cycler 14 is not level. When ALARM1 occurs, the controller 16 suspends the therapy session and soundε an audible alarm. The controller 16 also displays an ALARM MENU that informs the uεer about the condition that should be corrected. The ALARM MENU giveε the uεer the choice to correct the condition and CONTINUE; to END the therapy; or to BYPASS (i.e., ignore) the condition and resume the therapy sesεion. The controller 16 raiεeε ALARM2 in εituationε that are anomalieε but will typically correct themselves with minimum or no user intervention. For example, the controller 16 raises ALARM2 when the controller 16 initially senses a low flow or an occluded lines. In this situation, the patient might have rolled over onto the catheter and may need only to move to rectify the matter. When ALARM2 occurs, the controller 16 generateε a first audible signal (e.g., 3 beeps). The controller 16 then mutes the audible signal for 30 seconds. If the condition still exiεtε after 30 second, the controller 16 generates a second audible εignal (e.g., 8 beeps) The controller 16 again muteε the audible εignal. If the condition still existε 30 εeconds later, the controller 16 raiεeε an ALARM1, aε deεcribed above. The uεer is then required to intervene using the ALARM MENU. 9. POST THERAPY PROMPTS The controller 16 terminates the session when (a) the prescribed therapy εeεεion iε succesεfully completed; (b) the uεer εelects END in the STOP SUBMENU or the ALARM MENU; or (c) a SYSTEM ERROR condition occurs (see Fig. 31) . When any of these events occur, the controller 16 displays POST THERAPY PROMPTS to the user. The POST THERAPY PROMPTS inform the user THERAPY FINISHED, to CLOSE CLAMPS, and to DISCONNECT PATIENT. The uεer preεεeε GO to advance the promptε. Once the uεer diεconnectε the patient and presses GO, the controller 16 displayε PLEASE WAIT and depreεεurizeε the door. Then the controller 16 then directs the uεer to REMOVE SET. Once the user removes the εet and preεεeε GO, the controller 16 returns to user to the MAIN MENU. (B) Controlling an APD Therapy Cycle 1. Fill Phase In the fill phaεe of a typical three phaεe APD cycle, the cycler 14 tranεfers warmed dialyεate from the heater bag 22 to the patient. The heater bag 22 iε attached to the firεt (uppermost) casεette port 27. The patient line 34 iε attached to the fifth (bottommost) cassette port 35. As Fig. 32 shows, the fill phaεe involveε drawing warmed dialyεate into caεsette pump chamber Pl through primary liquid path FI via branch liquid path F6. Then, pump chamber Pl expels the heated dialysate through primary liquid path F5 via branch liquid path F8. To expedite pumping operations, the controller 16 preferably works pump chamber P2 in tandem with pump chamber Pl. The controller 16 draws heated dialysate into pump chamber P2 through primary liquid path FI via branch liquid path F7. Then, pump chamber P2 expels the heated dialysate through primary liquid path F5 through branch liquid path F9. The controller 16 works pump chamber Pl in a draw stroke, while working pump chamber P2 in a pump stroke, and vice versa. In this sequence, heated dialysate is always introduced into the top portions of pump chamberε Pl and P2. The heated dialyεate iε alwayε discharged through the bottom portions of pump chambers Pl and P2 to the patient free of air. Furthermore, during liquid transfer directly with the patient, the controller 16 can supply only low-relative positive and negative preεεureε to the pump actuators PAl and PA2. In carrying out this task, the controller 16 alternates the following sequences 1 and 2: 1. Perform pump chamber Pl draw stroke (drawing a volume of heated dialysate into pump chamber Pl from the heater bag) , while performing pump chamber P2 pump stroke (expelling a volume of heated dialysate from pump chamber P2 to the patient) . (i) Open inlet path FI to pump chamber Pl, while closing inlet path FI to pump chamber P2. Actuate valve CO to supply high-relative negative pressure to valve actuator VAl, opening cassette valve station VI. Actuate valves Cl; Dl; and D2 to supply high-relative positive preεεure to valve actuators VA2 ; VA3 : and VA4, closing cassette valve station V2; V3 ; and V4. (ii) Close outlet path F5 to pump chamber Pl, while opening outlet path F5 to pump chamber P2. Actuate valves C2 to C4 and D3 to D5 to supply high-relative positive pressure to valve actuators VA8 to VIO and VA5 to VA7 , closing cassette valve stations V8 to VIO and V5 to V7. Actuate valve D5 to supply high-relative negative pressure to valve actuator VA7, opening casεette valve εtation V7. (iii) Flex the diaphragm underlying actuator PAl out. Actuate valve AO to supply low- relative negative presεure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 in. Actuate valve Bl to εupply low- relative poεitive pressure to pump actuator PA2. 2. Perform pump chamber P2 draw stroke (drawing a volume of heated dialyεate into pump chamber P2 from the heater bag) , while performing pump chamber Pl pump εtroke (expelling a volume of heated dialysate from pump chamber Pl to the patient) . (i) Open inlet path FI to pump chamber P2, while closing inlet path FI to pump chamber Pl. Actuate valveε CO; Cl; and D2 to supply high- relative positive pressure to valve actuatorε VAl; VA2; and VA4 , cloεing caεεette valve εtationε VI; V2; and V4. Actuate valve Dl to εupply high- relative negative pressure to valve actuator VA3 , opening casεette valve station V3. (ii) Cloεe outlet path F5 to pump chamber P2, while opening outlet path F5 to pump chamber Pl. Actuate valve C2 to supply high-relative negative pressure to valve actuator VA8, opening cassette valve station V8. Actuate valveε D3 to D5; C2; and C4 to supply high-relative positive pressure to valve actuators VA5 to VA7; V9; and VIO, closing cassette valve stations V5 to V7; V9; and VIO. (iii) Flex the diaphragm underlying actuator PAl in. Actuate valve A3 to supply low- relative positive pressure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 out. Actuate valve B4 to supply low- relative negative pressure to pump actuator PA2. 2. Dwell Phase Once the programmed fill volume has been transferred to the patient, the cycler 14 enterε the second or dwell phase. In this phase, the cycler 14 replenisheε the heater bag by supplying fresh dialysate from a source bag. The heater bag is attached to the firεt (uppermost) cassette port. The source bag line is attached to the fourth casεette port, immediately above the patient line. Aε Fig. 33 εhowε, the repleniεh heater bag phase involves drawing fresh dialysate into casεette pump chamber Pl through primary liquid path F4 via branch liquid path F8. Then, pump chamber Pl expels the dialysate through primary liquid path FI via branch liquid path F6. To expedite pumping operations, the controller 16 preferably works pump chamber P2 in tandem with pump chamber Pl. The controller 16 draws fresh dialysate into cassette pump chamber P2 through primary liquid path F4 via branch liquid path F9. Then, pump chamber P2 expels the dialysate through primary liquid path FI via branch liquid path F7. The controller 16 works pump chamber Pl in a draw stroke, while working pump chamber P2 in a pump stroke, and vice versa. In this sequence, fresh dialysate is always introduced into the bottom portionε of pump chamberε Pl and P2. The freεh dialyεate iε alwayε diεcharged through the top portions of pump chambers Pl and P2 to the heater bag. This allows entrapped air to be removed from the pump chambers Pl and P2. Furthermore, εince liquid transfer does not occur directly with the patient, the controller 16 supplieε high-relative poεitive and negative preεεureε to the pump actuators PAl and PA2. In carrying out this task, the controller 16 alternates the following sequenceε: 1. Perform pump chamber Pl draw stroke (drawing a volume of freεh dialysate into pump chamber Pl from a source bag) , while performing pump chamber P2 pump stroke (expelling a volume of fresh dialysate from pump chamber P2 to the heater bag) . (i) Open inlet path F4 to pump chamber Pl, while closing inlet path F4 to pump chamber P2. Actuate valve C3 to supply high-relative negative pressure to valve actuator VA9, opening casεette valve station V9. Actuate valves D3 to D5; C2; and C4 to supply high-relative positive presεure to valve actuatorε VA5 to VA8; and VAIO, cloεing cassette valve stations V5 to V8 and VIO. (ii) Close outlet path FI to pump chamber Pl, while opening outlet path FI to pump chamber P2. Actuate valves CO; Cl; and D2 to εupply high- relative poεitive preεεure to valve actuatorε VAl; VA2 and VA4, cloεing caεεette valve εtations VI; V2; and V4. Actuate valve Dl to supply high-relative negative pressure to valve actuator VA3 , opening cassette valve station V3. (iii) Flex the diaphragm underlying actuator PAl out. Actuate valve AO to supply high- relative negative presεure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 in. Actuate valve BO to εupply high- relative positive pressure to pump actuator PA2. 2. Perform pump chamber P2 draw stroke (drawing a volume of freεh dialyεate into pump chamber P2 from a εource bag) , while performing pump chamber Pl pump stroke (expelling a volume of fresh dialyεate from pump chamber Pl to heater bag) . (i) Close inlet path F4 to pump chamber Pl, while opening inlet path F4 to pump chamber P2. Actuate valve D5 to supply high-relative negative pressure to valve actuator VA6, opening casεette valve station V6. Actuate valveε C3 to C4 ; D3 ; and D5 to supply high-relative poεitive pressure to valve actuators VA5 and VA7 to VAIO, closing cassette valve stationε V5 and V7 to VIO. (ii) Open outlet path FI to pump chamber Pl, while closing outlet path FI to pump chamber P2. Actuate valve CO to supply high-relative negative pressure to valve actuator VAl, opening casεette valve station VI. Actuate valves Cl; Dl; and D2 to εupply high-relative positive pressure to valve actuators VA2 to VA4 , cloεing caεεette valve εtation V2 to V4. (iii) Flex the diaphragm underlying actuator PAl in. Actuate valve A4 to εupply high- relative poεitive preεεure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 out. Actuate valve B4 to supply high- relative negative preεεure to pump actuator PA2. 3. Drain Phase When the programmed drain phaεe endε, the cycler 14 enterε the third or drain phaεe. In thiε phaεe, the cycler 14 tranεferε εpent dialyεate from the patient to a drain. The drain line iε attached to the second cassette port. The patient line is attached to the fifth, bottommost caεεette port. Aε Fig. 34 εhowε, the drain phaεe involveε drawing spent dialysate into casεette pump chamber Pl through primary liquid path F5 via branch liquid path F8. Then, pump chamber Pl expelε the dialyεate through primary liquid path F2 via branch liquid path F6. To expedite pumping operationε, the controller 16 workε pump chamber P2 in tandem with pump chamber Pl. The controller 16 drawε εpend dialyεate into caεεette pump chamber P2 through primary liquid path F5 via branch liquid path F9. Then, pump chamber P2 expelε the dialyεate through primary liquid path F2 via branch liquid path F7. The controller 16 workε pump chamber Pl in a draw εtroke, while working pump chamber P2 in a pump εtroke, and vice verεa. In thiε εequence, εpent dialyεate iε alwayε introduced into the bottom portionε of pump chambers Pl and P2. The spent dialyεate is always discharged through the top portions of pump chambers Pl and P2 to the heater bag. This allows air to be removed from the pump chamberε Pl and P2. Furthermore, εince liquid tranεfer doeε occur directly with the patient, the controller 16 εupplieε low-relative poεitive and negative preεsures to the pump actuatorε PAl and PA2. In carrying out this task, the controller 16 alternates the following sequences: 1. Perform pump chamber Pl draw stroke (drawing a volume of spent dialysate into pump chamber Pl from the patient) , while performing pump chamber P2 pump stroke (expelling a volume of spent dialysate from pump chamber P2 to the drain) . (i) Open inlet path F5 to pump chamber Pl, while closing inlet path F5 to pump chamber P2. Actuate valve C2 to supply high-relative negative pressure to valve actuator VA8, opening cassette valve station V8. Actuate valves D3 to D5, C3, and C4 to supply high-relative positive pressure to valve actuators VA5 to VA7, VA9 and VAIO, closing cassette valve stations V5 to V7, V9, and VIO. (ii) Close outlet path F2 to pump chamber Pl, while opening outlet path F2 to pump chamber P2. Actuate valves CO; Cl; and Dl to supply high- relative positive presεure to valve actuatorε VAl; VA2 and VA3, cloεing caεεette valve stationε VI; V2; and V3. Actuate valve D2 to supply high-relative negative pressure to valve actuator VA4, opening cassette valve station V4. (iii) Flex the diaphragm underlying actuator PAl out. Actuate valve AO to supply low- relative negative pressure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 in. Actuate valve Bl to supply low- relative positive preεεure to pump actuator PA2. 2. Perform pump chamber P2 draw stroke (drawing a volume of spent dialysate into pump chamber P2 from the patient) , while performing pump chamber Pl pump stroke (expelling a volume of spent dialysate from pump chamber Pl to the drain) . (i) Close inlet path F5 to pump chamber Pl, while opening inlet path F5 to pump chamber P2. Actuate valve D5 to εupply high-relative negative pressure to valve actuator VA7, opening casεette valve εtation V7. Actuate valveε D3; D4 and C2 to C4 to supply high-relative positive presεure to valve actuatorε VA5; VA6; and VA8 to VAIO, cloεing caεsette valve stations V5, V6, and V8 to VIO. (ii) Open outlet path F2 to pump chamber Pl, while closing outlet path F2 to pump chamber P2. Actuate valve Cl to supply high-relative negative presεure to valve actuator VA2, opening cassette valve station V2. Actuate valves CO; Dl; and D2 to supply high-relative poεitive preεεure to valve actuatorε VAl; VA3; and VA4, cloεing caεsette valve station VI; V3; and V4. (iii) Flex the diaphragm underlying actuator PAl in. Actuate valve A3 to supply low- relative poεitive preεεure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 out. Actuate valve B4 to εupply low- relative negative preεεure to pump actuator PA2. The controller 16 senses presεure using transducerε XP1 and XP2 to determine when the patient's peritoneal cavity iε empty. The drain phaεe iε followed by another fill phaεe and dwell phase, as previously deεcribed. 4. Last Dwell Phase In some APD procedures, like CCPD, after the last prescribed fill/dwell/drain cycle, the cycler 14 infuseε a final fill volume. The final fill volume dwellε in the patient through the day. It iε drained at the outεet of the next CCPD εession in the evening. The final fill volume can contain a different concentration of dextroεe than the fill volume of the succesεive CCPD fill/dwell/drain fill cycleε the cycler 14 provideε. The choεen dextroεe concentration sustainε ultrafiltration during the day-long dwell cycle. In thiε phase, the cycler 14 infuses fresh dialysate to the patient from a "last fill" bag. The "last fill" bag iε attached to the third cassette port. During the last εwell phaεe, the heater bag iε emptied, and εolution from laεt bag volume iε transferred to the heater bag. From there, the last fill solution is transferred to the patient to complete the laεt fill phase. The last dwell phase involves drawing liquid from the heater bag into pump chamber Pl through primary liquid path FI via branch path F6. The, the pump chamber Pl expels the liquid to the drain through primary liquid path F2 via branch liquid path F6. To expedite drainage of the heater bag, the controller 16 works pump chamber P2 in tandem with pump chamber Pl. The controller 16 draws liquid from the heater bag into pump chamber P2 through primary liquid path FI via branch liquid path F7. Then, pump chamber P2 expels liquid to the drain through primary liquid path F2 via branch liquid path F7. The controller 16 workε pump chamber Pl in a draw stroke, while working pump chamber P2 in a pump stroke, and vice versa. Once the heater bag is drained, the controller 16 draws fresh dialysate from the "last fill" bag into cassette pump chamber Pl through primary liquid path F3 via branch liquid path F8. Then, pump chamber Pi expels the dialysate to the heater bag through primary liquid path FI via the branch liquid path F6. Aε before, to expedite pumping operationε, the controller 16 preferably works pump chamber P2 in tandem with pump chamber Pl. The controller 16 draws fresh dialysate from the "laεt fill" bag into cassette pump chamber P2 through primary liquid path F3 via branch liquid path F9. Then, pump chamber P2 expels the dialyεate through primary liquid path FI via the branch liquid path F7. The controller 16 workε pump chamber Pl in a draw εtroke, while working pump chamber P2 in a pump stroke, and vice versa. In this εequence, fresh dialysate from the "laεt fill" bag is always introduced into the bottom portionε of pump chamberε Pl and P2. The freεh dialysate is alwayε diεcharged through the top portions of pump chambers Pl and P2 to the heater bag. This allows air to be removed from the pump chambers Pl and P2. Furthermore, εince liquid transfer does not occur directly with the patient, the controller 16 can supply high-relative positive and negative preεsures to the pump actuators PAl and PA2. In carrying out thiε taεk, the controller 16 alternateε the following εequenceε (εee Fig. 35) : 1. Perform pump chamber Pl draw εtroke (drawing a volume of freεh dialysate into pump chamber Pl from the "laεt fill" bag) , while performing pump chamber P2 pump εtroke (expelling a volume of freεh dialyεate from pump chamber P2 to the heater bag) . (i) Open inlet path F3 to pump chamber Pl, while closing inlet path F3 to pump chamber P2. Actuate valve C4 to supply high-relative negative pressure to valve actuator VAIO, opening casεette valve station VIO. Actuate valves D3 to D5; C2; and C3 to supply high-relative positive pressure to valve actuators VA5 to VA9, cloεing caεεette valve stations V5 to V9. (ii) Close outlet path FI to pump chamber Pl, while opening outlet path FI to pump chamber P2. Actuate valves CO; Cl; and D2 to supply high- relative positive presεure to valve actuators VAl; VA2 and VA4, closing casεette valve εtationε VI; V2; and V4. Actuate valve Dl to εupply high-relative negative pressure to valve actuator VA3, opening cassette valve station V3. (iii) Flex the diaphragm underlying actuator PAl out. Actuate valve AO to supply high- relative negative pressure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 in. Actuate valve BO to supply high- relative positive presεure to pump actuator PA2. 2. Perform pump chamber P2 draw εtroke (drawing a volume of freεh dialyεate into pump chamber P2 from the "laεt fill" bag) , while performing pump chamber Pl pump εtroke (expelling a volume of fresh dialysate from pump chamber Pl to heater bag) . (i) Close inlet path F3 to pump chamber Pl, while opening inlet path F3 to pump chamber P2. Actuate valve D3 to εupply high-relative negative pressure to valve actuator VA5, opening caεεette valve station V5. Actuate valveε C2 to C4; D4; and D5 to supply high-relative positive pressure to valve actuatorε VA6 to VAIO, cloεing caεεette valve εtationε V6 to VIO. (ii) Open outlet path FI to pump chamber Pl, while cloεing outlet path FI to pump chamber P2. Actuate valve CO to εupply high-relative negative pressure to valve actuator VAl, opening cassette valve station VI. Actuate valves Cl; Dl; and D2 to supply high-relative positive pressure to valve actuators VA2 to VA4, closing caεεette valve εtation V2 to V4. (iii) Flex the diaphragm underlying actuator PAl in. Actuate valve A4 to εupply high- relative positive presεure to pump actuator PAl. (iv) Flex the diaphragm underlying actuator PA2 out. Actuate valve B4 to supply high- relative negative presεure to pump actuator PA2. Once the last fill solution has been heated, it is transferred to the patient in a fill cycle as described above (and aε Fig. 32 εhows) . According to one aspect of the invention, every important aspect of the APD procedure is controlled by fluid presεure. Fluid preεεure moveε liquid through the delivery set, emulating gravity flow conditions based upon either fixed or variable headheight conditions. Fluid presεure controlε the operation of the valveε that direct liquid among the multiple deεtinationε and εourceε. Fluid preεsure serves to seal the casεette within the actuator and provide a failsafe occlusion of the aεεociated tubing when conditionε warrant. Fluid preεεure is the basiε from which delivered liquid volume meaεurements are made, from which air entrapped in the liquid is detected and elimination, and from which occluded liquid flow conditions are detected and diagnosed. According to another aspect of the invention, the cassette serves to organize and mainfold the multiple lengths of tubing and bagε that peritoneal dialyεiε requireε. The caεsette alεo εerves to centralize all pumping and valving activitieε required in an automated peritoneal dialyεiε procedure, while at the same time serving as an effective sterility barrier, Various features of the invention are set forth in the following claims.

Claims: We Claim: 1. A method for performing peritoneal dialysiε comprising the stepε of establishing flow communication with the patient's peritoneal cavity through a pumping mechanism that compriseε a pump chamber and a diaphragm, and emulating a selected gravity flow condition by applying fluid pressure to the diaphragm to operate the pump chamber to either move dialysiε εolution fluid from the peritoneal cavity or move dialyεiε εolution into the peritoneal cavity. 2. A method according to claim 1 wherein, in applying fluid preεsure, a fixed head height condition iε emulated. 3. A method according to claim 1 wherein, in applying fluid preεεure, the magnitude of the applied fluid presεure iε changed to emulate different head height conditionε. 4. A method according to claim 1 wherein, in applying fluid pressure, pneumatic fluid pressure is applied. 5. A method according to claim 1 wherein, in applying fluid pressure, a fluid pressure that is below atmospheric pressure is applied. 6. A method according to claim 1 wherein, in applying fluid presεure, a fluid preεεure that iε above atmospheric preεsure is applied. 7. A method according to claim 1 and further including the steps of normally isolating the patient's peritoneal cavity from the pump chamber by a valve, and selectively opening the valve to accommodate movement of the dialyεis solution to and from the patient's peritoneal cavity. 8. A method according to claim 7 wherein, in the step of opening and closing the valve, fluid pressure is applied. 9. A method according to claim 7 wherein, in opening and closing the valve, pneumatic pressure is applied. 10. A method for performing peritoneal dialysis comprising the εtepε of establishing flow communication with the patient's peritoneal cavity through a pumping mechanism that comprises a pump chamber, at least one valve communicating with the pump chamber, and a diaphragm, and emulating a selected gravity flow condition by applying fluid pressure to the diaphragm to operate the pump chamber and valve to move dialysiε solution from the peritoneal cavity to a drain or move fresh dialysiε solution from a source into the peritoneal cavity. 11. A method according to claim 10 wherein, in applying fluid pressure, a fixed head height condition is emulated. 12. A method according to claim 10 wherein, in applying fluid presεure, the magnitude of the applied fluid preεsure is changed to emulate different head height conditions. 13. A method according to claim 10 wherein, in applying fluid presεure, pneumatic presεure iε applied. 14. A method according to claim 10 wherein, in applying fluid preεsure, a fluid pressure that is below atmospheric pressure is applied. 15. A method according to claim 10 wherein, in applying fluid preεεure, a fluid pressure that is above atmospheric presεure iε applied. 16. A method for performing peritoneal dialysis comprising the stepε of establishing flow communication between the patient's peritoneal cavity and an external component through a pumping mechanism that comprises a pump chamber and a diaphragm, and applying fluid presεure to the diaphragm to operate the pump chamber to move dialysiε solution between the external component and the patient's peritoneal cavity at a flow condition that emulates a selected head height differential between the external component and the patient's peritoneal cavity independent of the actual head height differential between the external component and the patient's peritoneal cavity. 17. A method according to claim 16 wherein, in applying fluid presεure, the magnitude of the applied fluid pressure is changed to emulate different head height differentials independent of the actual head height differential between the external component and the patient's peritoneal cavity. 18. A method according to claim 16 wherein, in applying fluid pressure, pneumatic presεure iε applied. 19. A method according to claim 16 wherein, in applying fluid pressure, a fluid presεure that iε below atmoεpheric preεεure iε applied. 20. A method according to claim 16 wherein, in applying fluid pressure, a fluid pressure that is above atmoεpheric pressure is applied. 21. A method for performing peritoneal dialysis comprising the stepε of eεtablishing flow communication among the patient's peritoneal cavity, a source of dialyεis solution, and a drain through a pumping mechanism that comprises a pump chamber, at least one valve communicating with the pump chamber, and a diaphragm, and emulating a selected gravity flow condition by applying fluid pressure to the diaphragm to operate the pump chamber and valve to: (i) direct spent dialysiε solution from the patient's peritoneal cavity into the pump chamber, (ii) direct the spent dialysiε solution from the pump chamber to the drain, (iii) direct fresh dialysiε solution from the source into the pump chamber, and (iv) direct the fresh dialysis solution from the pump chamber to the patient's peritoneal cavity. 22. A method according to claim 21 wherein, in at least one of the stepε (i) and (iv) , the magnitude of the applied fluid pressure is different than the magnitude of the applied fluid preεεure in another one of the εtepε (ii) or (iii) . 23. A method according to claim 21 and further including the εtep of varying the magnitude of the applied fluid preεsure to emulate different head height conditionε. 24. A method according to claim 21 wherein, in applying fluid pressure, pneumatic pressure iε applied. 25. A method for performing peritoneal dialysis comprising the steps of establishing flow communication among the patient's peritoneal cavity, a source of fresh dialysis solution, a reservoir for heating the fresh dialysis solution, and a drain through a pumping mechanism that compriseε a pump chamber, at least one valve communicating with the pump chamber, and a diaphragm, and emulating a selected gravity flow condition by applying fluid pressure to the diaphragm to operate the pump chamber and valve to (i) direct spent dialysiε solution from the patient's peritoneal cavity into the pump chamber, (ii) direct the spent dialysiε solution from the pump chamber to the drain, (iii) direct fresh dialysiε εolution from the source into the pump chamber, (iv) direct the fresh dialysiε solution from the pump chamber to the reservoir for heating, (v) direct the heated fresh dialysiε solution from the reservoir into the pump chamber, and (vi) direct the heated fresh dialysiε εolution from the pump chamber to the patient's catheter. 26. A method according to claim 25 wherein, in at leaεt one of the steps (i) and (vi) , the magnitude of the applied fluid presεure is lesε than the magnitude of the fluid pressure applied in another one of the stepε (ii) to (v). 27. A method according to claim 25 and further including the step of varying the magnitude of the applied fluid preεsure to emulate different head height conditions. 28. A method according to claim 25 wherein, in applying fluid pressure, pneumatic preεεure iε applied. 29. A method according to claim 25 wherein εteps (i) to (vi) are cycled in succession at least two times. 30. A method according to claim 29 wherein, in the last cycle of steps, the dialysis solution directed into the patient's peritoneal cavity in steps (iii) to (vi) has a different composition than the composition of the dialysis solution directed into the patient's peritoneal cavity during stepε (iii) to (vi) in the firεt cycle of stepε. 31. A method for performing peritoneal dialysis comprising the steps of establishing flow communication with the patient's peritoneal cavity through a pumping mechanism that comprises a pump chamber and a diaphragm, and emulating a selected gravity flow condition by applying pneumatic pressure to the diaphragm through an actuator to operate the pump chamber to draw dialysiε εolution into the pump chamber and to expel dialyεis solution from the pump chamber to either move dialysiε εolution from the peritoneal cavity or move dialyεis εolution into the peritoneal cavity, and deriving a meaεurement of liquid volume pumped through the pump chamber by deriving an initial air volume measurement V j after operating the actuator to draw fluid into the pumping chamber; deriving a final air volume measurement Vf after operating the actuator to expel fluid from the pumping chamber; and deriving the liquid volume delivered (V d ) by the pumping chamber as follows: V d = V f - V j , and wherein V- and Vf are derived by controlling communication between a reference chamber having a known air volume V s and the actuator by: (i) when liquid is either drawn into or expelled from the pump chamber, cloεing communication between reference chamber and the actuator to initialize the reference chamber to a measured initial air pressure (IP sj ) while applying a measured preεεure to the actuator (IPdl- 1 ' (ϋ) ^-^ n opening communication between the reference chamber and the actuator to allow preεsure equilibration at a measured new air presεure in the actuator (IP d 2) and a meaεured new air pressure in the reference chamber (IP s -j) , and (iii) then deriving the air volume measurement V j or Vf as follows: 32. A system for performing peritoneal dialysiε compriεing a pumping mechaniεm comprising a diaphragm, means for establishing flow communication with the patient's peritoneal cavity through the pumping mechanism, and actuating means for emulating a selected gravity flow condition by applying fluid presεure to the diaphragm to operate the pumping mechanism to either move dialysiε solution from the peritoneal cavity or move dialysiε solution into the peritoneal cavity, and control means selectively operating the actuating means for applying fluid pressure to emulate either a fixed head height condition or different head height conditions. 33. A system according to claim 32 wherein the actuating means applies pneumatic fluid pressure. 34. A system according to claim 32 wherein the actuating means applies fluid pressure that is below atmospheric preεεure. 35. A εyεtem according to claim 32 wherein the actuating meanε applies fluid pressure that is above atmospheric preεεure. 36. A system according to claim 32 wherein, in a first mode of operation, the actuating meanε applieε a first magnitude of fluid pressure and, in a second mode of operation, the actuating means applies a second magnitude of fluid pressure different than the first magnitude. 37. A system according to claim 32 and further including valve means for normally isolating the patient's peritoneal cavity from the pumping mechanism including means for selectively opening the valve means to accommodate movement of the dialysis solution to and from the patient's peritoneal cavity. 38. A syεtem according to claim 37 wherein the valve meanε is operated in responεe to fluid preεsure. 39. A εyεtem according to claim 37 wherein the valve meanε iε operated in response to pneumatic presεure. 40. A peritoneal dialyεiε system comprising a pumping mechanism comprising a pump chamber, at leaεt one valve communicating with the pump chamber, and a diaphragm, meanε for eεtabliεhing flow communication between the pumping mechaniεm and the patient'ε peritoneal cavity, actuating means for emulating gravity flow conditionε by applying fluid preεεure to the diaphragm to operate the pump chamber and valve to: (i) drain εpent peritoneal dialyεiε εolution from the patient'ε peritoneal cavity, and (ii) infuεe fresh dialyεiε εolution from a εource into the patient'ε peritoneal cavity, and control meanε εelectively operating the actuating means for applying fluid presεure to emulate either a fixed head height condition or different head height conditions. 41. A εyεtem according to claim 40 wherein the actuating meanε applieε pneumatic fluid preεεure. 42. A εyεtem according to claim 40 wherein the actuating meanε applieε fluid preεεure that iε below atmoεpheric preεεure. 43. A εyεtem according to claim 40 wherein the actuating meanε applieε fluid pressure that iε above atmoεpheric pressure. 44. A syεtem according to claim 40 wherein, in a firεt mode of operation, the actuating meanε applieε a firεt magnitude of fluid pressure and, in a second mode of operation, the actuating means applies a second magnitude of fluid pressure different than the firεt magnitude. 45. A peritoneal dialyεiε system comprising means defining a pump chamber that has a diaphragm, patient conduit means for establishing flow communication between the pump chamber and the patient's peritoneal cavity, an other conduit means for establishing flow communication between the pump chamber and an external component outside the patient's peritoneal cavity, meanε for applying fluid preεεure to the diaphragm to pump dialysis solution through the patient conduit means and the other conduit means, and presεure regulation means for applying fluid pressure variations to the diaphragm of a first magnitude when liquid is conveyed through the patient conduit means and for applying fluid pressure to the diaphragm of a second magnitude different than the firεt magnitude when liquid iε conveyed through the other conduit meanε. 46. A εyεtem according to claim 45 wherein the firεt magnitude iε leεε than the second magnitude. 47. A system according to claim 45 and further including meanε for varying the agnitudeε of the presεure applied to the diaphragm to emulate different head height conditionε. 48. A εyεtem according to claim 45 wherein the actuating meanε applieε pneumatic pressure. 49. A syεtem according to claim 45 wherein the actuating means applies fluid pressure that is below atmospheric pressure. 50. A system according to claim 45 wherein the actuating meanε applieε fluid preεsure that iε above atmoεpheric pressure. 51. A fluid diεtribution system for conducting peritoneal dialysis comprising a casεette having a body, meanε in caεεette body for defining first and second pump chambers, diaphragm means associated with both pump chambers on the casεette body and operative in response to externally applied fluid pressure variations for moving liquid through the pump chamberε, meanε in the caεεette body defining firεt and εecond fluid pathε communicating with the firεt and second pump chamberε, reεpectively, for conveying liquid through the respective pump chamberε when preεεure variationε are applied to the diaphragm meanε, and preεsure regulation meanε for applying fluid pressure to the diaphragm means associated with the first pump chamber at a first magnitude while applying fluid presεure to the diaphragm means associated with the second pump chamber at a second magnitude different than the first magnitude to convey liquid through the first pump chamber at a different presεure than through the εecond pump chamber. 52. A peritoneal dialysis system comprising means defining a pump chamber that has a diaphragm, conduit means for establiεhing flow communication among the patient's peritoneal cavity, a source of fresh dialysiε εolution, and a drain through the pump chamber, actuating meanε for applying fluid pressure to the diaphragm to move spent peritoneal dialysis solution from the patient's peritoneal cavity to the drain through the pump chamber and to pump fresh dialysis solution from the source to the patient's peritoneal cavity through the pump chamber, meanε for directing fluid flow through the pump chamber including meanε for directing εpent peritoneal dialysis solution from the patient's peritoneal cavity into the pump chamber, means for directing the spent dialysis solution from the pump chamber to the drain, means for directing fresh dialysiε solution from the source into the pump chamber, and meanε for directing the fresh dialysis solution from the pump chamber to the patient's peritoneal cavity, and pressure regulation means for applying fluid pressure to the diaphragm of a first magnitude when liquid is conveyed through the pump chamber to and from the patient's peritoneal cavity and for applying fluid presεure variationε to the diaphragm of a second magnitude different than the first magnitude when liquid is conveyed through the pump chamber either to the drain or from the source container. 53. A system according to claim 52 and further including means for adjusting the magnitude of the fluid preεεure variationε applied to the diaphragm to emulate different head height conditions. 54. A system according to claim 51 wherein the actuating means applieε pneumatic pressure. 55. A system according to claim 52 wherein the actuating means applies fluid pressure that is below atmospheric pressure. 56. A system according to claim 52 wherein the actuating means applies fluid presεure that iε above atmoεpheric preεεure. 57. A peritoneal dialyεis εyεtem compriεing means defining a pump chamber that haε a diaphragm, conduit meanε for establiεhing flow communication among the patient's peritoneal cavity, a source of fresh dialysiε εolution, a reεervoir for heating the freεh dialysis solution, and a drain through the pump chamber, actuating means for applying fluid pressure to the diaphragm to move liquid through the pump chamber, means for directing liquid flow through the pump chamber including meanε for directing εpent peritoneal dialyεiε solution from the patient's peritoneal cavity into the pump chamber, means for directing the spent dialysis solution from the pump chamber to the drain, meanε for directing freεh dialyεiε solution from the source into the pump chamber, means for directing the fresh dialyεis solution from the pump chamber to the reservoir for heating, means for directing the heated fresh dialysis solution from the reεervoir into the pump chamber, and meanε for directing the heated fresh dialysis solution from the pump chamber to the patient's peritoneal cavity, and pressure regulation means for applying fluid pressure to the diaphragm of a first magnitude when liquid is conveyed through the pump chamber to and from the patient's peritoneal cavity and for applying fluid pressure to the diaphragm of a second magnitude different than the first magnitude when liquid iε conveyed through the pump chamber either to the drain; or from the εource container; or to and from the reεervoir. 58. A εyεtem according to claim 57 and further including meanε for adjuεting the fluid pressure applied to the diaphragm to emulate different head height conditions. 59. A system according to claim 59 wherein the means for establiεhing flow communication includeε patient conduit meanε for eεtablishing flow communication between the pump chamber and the patient's peritoneal cavity, and an other conduit means for establishing flow communication between the pump chamber and a component other than the patient's peritoneal cavity, and wherein the actuator includeε pressure regulation meanε for the pressure conveying meanε to convey fluid preεεure to the diaphragm of a firεt magnitude when liquid iε moved through the patient conduit meanε and to convey fluid preεεure to the diaphragm of a second magnitude different than the first magnitude when liquid is moved through the other conduit means. 60. A syεtem according to claim 60 wherein the firεt magnitude of fluid preεεure iε leεε than the second magnitude of fluid pressure. 61. A system according to claim 59 wherein the actuator includeε control means for the preεεure conveying meanε operable in a first mode for conveying fluid pressure to emulate a fixed head height condition. 62. A syεtem according to claim 62 wherein the control means is operable in a second mode for varying the magnitude of the conveyed fluid presεure to emulate different head height conditionε. 63. A system according to claim 59 wherein the presεure conveying meanε conveyε pneumatic pressure. 64. A syεtem according to claim 59 wherein the preεεure conveying meanε conveyε fluid pressure that is below atmoεpheric pressure. 65. A εyεtem according to claim 59 wherein the pressure conveying means applieε fluid preεεure that iε above atmoεpheric preεsure. 66. A syεtem for performing peritoneal dialysiε compriεing a pumping mechaniεm compriεing a diaphragm, meanε for eεtabliεhing flow communication with the patient'ε peritoneal cavity through the pumping mechaniεm, and actuating means for emulating a selected gravity flow condition by applying pneumatic fluid pressure to the diaphragm to operate the pumping mechanism to either move dialysis solution from the peritoneal cavity or move dialysis fluid into the peritoneal cavity, the actuating means including a chamber for receiving pneumatic preεεure and inεert means occupying the chamber for stabilizing the applied pneumatic pressure within the chamber. 67. A system according to claim 66 wherein the insert is made of an open cell porous material.

Inventors: KAMEN DEAN, SPENCER GEOFFREY P, VINCENT DOUGLAS E, KAMEN, DEAN, SPENCER, GEOFFREY, P., VINCENT, DOUGLAS, E.
Applicants: DEKA PRODUCTS LP, DEKA PRODUCTS LIMITED PARTNERSHIP
Application year: 1994
Main classification: A61M1
IPC codes: A61M1, A61M5